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SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 10-K

x  Annual Report Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

For the fiscal year ended December 26, 2004

or

¨  Transition Report Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

For the transition period from                      to                     

Commission File Number 1-4825

WEYERHAEUSER COMPANY

A WASHINGTON CORPORATION

91-0470860

(IRS Employer Identification No.)

FEDERAL WAY, WASHINGTON 98063-9777 TELEPHONE (253) 924-2345

SECURITIES REGISTERED PURSUANT TO SECTION 12(B) OF THE ACT:

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.  xYes    ¨  No.

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant’s knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K.  ¨.

Indicate by check mark whether the registrant is an accelerated filer (as defined in Rule 12b-2 of the Act).  xYes    ¨  No.

As of June 25, 2004, 239,395,184 shares of the registrant’s common stock ($1.25 par value) were outstanding and the aggregate market value of the registrant’s voting shares held by non-affiliates was approximately $14,435,529,595.

As of January 28, 2005, 240,466,236 shares of the registrant’s common stock ($1.25 par value) were outstanding.

DOCUMENTS INCORPORATED BY REFERENCE

Portions of the Notice of Annual Meeting of Shareholders and Proxy Statement for the company’s Annual Meeting of Shareholders to be held April 21, 2005, are incorporated by reference into Part II and III.

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DESCRIPTION OF THE BUSINESS OF THE COMPANY

Weyerhaeuser Company (the company) was incorporated in the state of Washington in January 1900 as Weyerhaeuser Timber Company. It is principally engaged in the growing and harvesting of timber; the manufacture, distribution and sale of forest products; and real estate development and construction. Its business segments are:

Throughout this document, the term “company” refers to Weyerhaeuser Company and all of its majority-owned domestic and foreign subsidiaries and variable interest entities of which Weyerhaeuser Company or its subsidiaries are determined to be the primary beneficiary. The term “Weyerhaeuser” refers to the forest products-based operations and excludes the Real Estate and Related Assets operations.

The company has approximately 53,600 employees, of whom 52,200 are employed by Weyerhaeuser, and of this number, approximately 23,000 are covered by collective bargaining agreements, which generally are negotiated on a multi-year basis. Approximately 1,400 of the company’s employees are involved in the activities of its Real Estate and Related Assets segment.

The major markets, both domestic and foreign, in which Weyerhaeuser sells its products are highly competitive, with numerous strong sellers competing in each. Many of Weyerhaeuser’s products also compete with substitutes for wood and wood fiber products. The company’s subsidiaries in the Real Estate and Related Assets segment operate in highly competitive markets, competing with numerous regional and national firms in real estate development and construction and other real estate related activities. The company competes in its markets primarily through price, product quality and service levels.

In recent years, the company has grown substantially through acquisitions with the purchases of MacMillan Bloedel in 1999, Trus Joist International (Trus Joist) in 2000, and Willamette Industries, Inc. (Willamette) in 2002.

In 2004, the company’s sales to customers outside the United States totaled $4.3 billion (including exports of $1.8 billion from the United States, $1.9 billion of Canadian export and domestic sales and $0.6 billion of other foreign sales), or 19 percent of total consolidated sales and revenues, compared with 18 percent in 2003. All sales to customers outside the United States are subject to risks related to international trade and to political, economic and other factors that vary from country to country.

Financial information with respect to industry segments and geographical areas is included in Notes 23 and 24 of Notes to Financial Statements in “Financial Statements and Supplementary Data” below.

AVAILABLE INFORMATION

The company is subject to the information reporting requirements of the Securities Exchange Act of 1934 (the Exchange Act) and the company files periodic reports, proxy statements and other information with the Securities and Exchange Commission (SEC) relating to the company’s business, financial results and other matters. The reports, proxy statements and other information the company files may be inspected and copied at prescribed rates at the SEC’s Public Reference Room at 450 Fifth Street NW, Washington, D.C. 20549. You may obtain information on the operation of the SEC’s Public Reference Room by calling the SEC at 1-800-SEC-0330. The SEC also maintains an internet site that contains reports, proxy statements and other information regarding issuers like the company that file electronically with the SEC. The

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address of the SEC’s internet site is www.sec.gov. The company also posts its reports, proxy statements and other information that are transmitted electronically to the SEC on the company’s internet site as soon as reasonably practicable after such material is filed with, or furnished to, the SEC and such information is available free of charge. The company’s internet site is www.weyerhaeuser.com.

BUSINESS SEGMENTS

TIMBERLANDS

Weyerhaeuser is engaged in the management of 6.4 million acres of company-owned and .8 million acres of leased commercial forestland in North America (4.2 million acres in the southern United States and 3.0 million acres in the Pacific Northwest and Canada), most of it highly productive and located extremely well to serve both domestic and international markets. Weyerhaeuser also has renewable, long-term licenses on 30.4 million acres of forestland located in five provinces throughout Canada that are managed by its Canadian operations. The standing timber inventory on these lands is approximately 468 million cunits (a cunit is 100 cubic feet of solid wood). The relationship between cubic measurement and the quantity of end products that may be produced from timber varies according to the species, size and quality of timber, and will change through time as the mix of these variables changes. The end products are generally measured in board feet for lumber and square feet for panel products. To sustain the timber supply from its fee timberlands, Weyerhaeuser is engaged in extensive planting, suppression of nonmerchantable species, precommercial and commercial thinning, fertilization, and operational pruning, all of which increase the yield from its fee timberland acreage.

Weyerhaeuser accounts for the revenues and expenses associated with the management of company-owned and leased forestland in its Timberlands segment. Revenues and expenses associated with the management of licensed forestlands are included with the results of the operations they support, generally in the Wood Products segment.

Weyerhaeuser also manages forestlands in the Southern Hemisphere. The results of these international operations are included in the Corporate and Other segment.

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WOOD PRODUCTS

Weyerhaeuser’s wood products businesses produce and sell softwood lumber, plywood, veneer, composite panels, oriented strand board, hardwood lumber, and engineered lumber products. These products are sold primarily through Weyerhaeuser’s own sales organizations and building materials distribution business. The raw materials required to produce these products are purchased from third parties, transferred at market price from Weyerhaeuser’s Timberlands segment, or obtained from long-term licensing arrangements. Building materials, including products not produced by Weyerhaeuser, are sold to wholesalers, retailers and industrial users.

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PULP AND PAPER

Weyerhaeuser’s pulp and paper businesses include: Pulp, which includes the manufacture of papergrade, absorbent, dissolving and specialty pulp grades that are marketed worldwide; Paper, which manufactures a range of both coated and uncoated papers and business forms marketed through Weyerhaeuser’s own sales force and through paper merchants and printers; and Liquid Packaging, which includes the manufacture and sales of liquid packaging board used primarily in the production of containers designed to hold liquid products.

In addition, Weyerhaeuser has a 50 percent interest in North Pacific Paper Corporation (NORPAC), a joint venture that owns a newsprint manufacturing facility in Washington state.

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CONTAINERBOARD, PACKAGING AND RECYCLING

Weyerhaeuser’s containerboard, packaging and recycling businesses include: Containerboard, which manufactures linerboard, corrugating medium and kraft paper, primarily used to produce corrugated boxes and paper bags and sacks at Weyerhaeuser’s packaging facilities and also sells product to domestic and foreign customers through Weyerhaeuser’s own sales force and agents; Packaging, which manufactures industrial and agricultural packaging marketed through Weyerhaeuser’s own sales force; Specialty Packaging, which produces inks, printing plates, graphics packaging, single-face and pre-print products, and retail packaging displays; and Recycling, which operates an extensive wastepaper collection system and sells to company mills and worldwide customers. The segment also operates facilities that manufacture paper bags and sacks.

REAL ESTATE AND RELATED ASSETS

The Real Estate and Related Assets segment includes Weyerhaeuser Real Estate Company (WRECO), a wholly-owned subsidiary, and the company’s other real estate related activities. WRECO is primarily engaged in developing single-family housing and residential lots for sale, including development of master-planned communities. Operations are concentrated mainly in selected metropolitan areas in southern California, Nevada, Washington, Texas, Maryland and Virginia. Additionally, WRECO is an investor and investment manager for institutional investors in residential real estate.

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CORPORATE AND OTHER

Corporate and Other includes marine transportation (Westwood Shipping Lines, a wholly-owned subsidiary), distribution and converting facilities located outside North America, and general corporate support activities.

The following international operations are included in Corporate and Other:

NATURAL RESOURCE AND ENVIRONMENTAL MATTERS

Growing and harvesting timber are subject to numerous laws and government policies to protect the environment, nontimber resources such as wildlife and water, and other social values. Changes in those laws and policies can significantly affect local or regional timber harvest levels and market values of timber-based raw materials.

In the United States, a number of fish and wildlife species that inhabit geographic areas near or within company timberlands have been listed as threatened or endangered under the federal Endangered Species Act (ESA) or similar state laws. Federal ESA listings include the northern spotted owl, marbled murrelet, a number of salmon species, bull trout and

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steelhead trout in the Pacific Northwest and the red-cockaded woodpecker, gopher tortoise and American burying beetle in the Southeast. Listings of additional species or populations may result from pending or future citizen petitions or be initiated by federal or state agencies. Federal and state requirements to protect habitat for threatened and endangered species have resulted in restrictions on timber harvest on some timberlands, including some timberlands of the company. Additional listings of fish and wildlife species as endangered, threatened or sensitive under the ESA and similar state laws as well as regulatory actions taken by federal or state agencies to protect habitat for these species may, in the future, result in additional restrictions on timber harvests and other forest management practices, could increase operating costs, and could affect timber supply and prices.

In the United States, federal, state and local regulations protecting water quality and wetlands also could affect future harvest and forest management practices on some of the company’s timberlands. Forest practice acts in some states in the United States increasingly affect present or future harvest and forest management activities. For example, in some states, these acts limit the size of clearcuts, require some timber to be left unharvested to protect water quality and fish and wildlife habitat, regulate construction and maintenance of forest roads, require reforestation following timber harvest, and contain procedures for state agencies to review and approve proposed forest practice activities. Some states and some local governments regulate certain forest practices through various permit programs. Each state in which the company owns timberlands has developed best management practices to reduce the effects of forest practices on water quality and aquatic habitats. Additional and more stringent regulations may be adopted by various state and local governments to achieve water-quality standards under the federal Clean Water Act, protect fish and wildlife habitats, or achieve other public policy objectives.

The company operates under the Sustainable Forestry Initiative^®, a certification standard designed to supplement government regulatory programs with voluntary landowner initiatives to further protect certain public resources and values. The Sustainable Forestry Initiative^® is an independent standard, overseen by a governing board consisting of conservation organizations, academia, the forest industry, and large and small forest landowners. Compliance with the Sustainable Forestry Initiative^® may result in some increases in operating costs and curtailment of timber harvests in some areas.

The regulatory and nonregulatory forest management programs described above have increased operating costs, resulted in changes in the value of timber and logs from the company’s timberlands, and contributed to increases in the prices paid for wood products and wood chips during periods of high demand. These kinds of programs also can make it more difficult to respond to rapid changes in markets, extreme weather or other unexpected circumstances. One additional effect may be further reductions in usage of, and some substitution of other products for, lumber and plywood. The company does not believe that these kinds of programs have had, or in 2005 will have, a significant effect on the company’s total harvest of timber in the United States or any major U.S. region, although they may have such an effect in the future. Further, the company does not expect to be disproportionately affected by these programs as compared with typical owners of comparable timberlands. Likewise, management does not expect that these programs will significantly disrupt its planned operations over large areas or for extended periods.

Weyerhaeuser’s forest operations in Canada are primarily carried out on public forestlands under forest licenses, although the company also owns substantial amounts of timberland in western British Columbia (B.C.). The announced sale of B.C. timberlands is expected to close in the second quarter of 2005. All forest operations are subject to forest practices and environmental regulations, and operations under licenses also are subject to contractual requirements between the company and the relevant province designed to protect environmental and other social values. In Canada, the federal Species at Risk Act (SARA) was enacted in 2002. SARA enacted protective measures for species identified as being at risk and for critical habitat. To date, SARA has not had an effect on the operations of the company; however, it is anticipated that SARA will result in some additional restrictions on timber harvests and other forest management practices and will increase some operating costs for operators of forestlands in Canada. SARA is also expected to affect timber supply and prices in the future.

The company participates in the Canadian Standards Association Sustainable Forest Management System standard, a voluntary certification system that further protects certain public resources and values. Compliance with this standard will result in some increases in operating costs and curtailment of timber harvests in some areas in Canada.

Many of these Canadian forestlands also are subject to the constitutionally protected treaty or common-law rights of the aboriginal peoples of Canada. Most of B.C. is not covered by treaties and, as a result, the claims of B.C.’s aboriginal peoples

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relating to forest resources are largely unresolved, although many aboriginal groups are actively engaged in treaty discussions with the governments of B.C. and Canada. Final or interim resolution of aboriginal claims may be expected to result in a negotiated decrease in the lands or timber available for forest operations under license in B.C., including the company’s licenses. In a case brought by the Council of Haida Nations against B.C., the Supreme Court of Canada ruled in 2004 that the province of B.C. has legally enforceable duties to the Haida to consult with and accommodate them with respect to forestry activities on the Queen Charlotte Islands. In October 2004, the Lyackson First Nation registered an objection to the proposed subdivision by the company of privately owned lands on Valdes Island in B.C. on the basis that the Lyackson First Nations’ aboriginal interests had not been sufficiently addressed. In December 2004, the Hupacasath First Nation petitioned a court of general jurisdiction in B.C. for a declaration that the province had failed to meaningfully consult with them before deciding to remove private lands owned by the company from a company Tree Farm License, and that they have aboriginal interests in these lands. The negotiation and resolution of aboriginal land claims and any claim such as those brought by these aboriginal groups are expected to result in additional restrictions on the sale or harvest of timber and may increase operating costs and affect timber supply and prices in Canada. The company believes that such claims will not have a significant effect on the company’s total harvest of timber or production of forest products in 2005, although they may have such an effect in the future.

The company is also subject to federal, state and provincial, and local pollution controls with regard to air, water and land; solid and hazardous waste management, disposal and remediation laws and regulations in all areas in which it has operations; as well as market demands with respect to chemical content of some products and use of recycled fiber. Compliance with these laws, regulations and demands usually involves capital expenditures as well as additional operating costs. The company cannot easily quantify future amounts of capital expenditures required to comply with these laws, regulations and demands, or the effects on operating costs, because in some instances, compliance standards have not been developed or have not become final or definitive. In addition, compliance with standards frequently serves other purposes such as extension of facility life, increase in capacity, changes in raw material requirements, or increase in economic value of assets or products. While it is difficult to isolate the environmental component of most manufacturing capital projects, the company estimates that capital expenditures for environmental compliance were approximately $46 million in 2004 (9 percent of total capital expenditures, excluding acquisitions and Real Estate and Related Assets). Based on its understanding of current regulatory requirements in the United States and Canada, the company expects that capital expenditures for environmental compliance will be approximately $44 million in 2005 (5 percent of expected total capital expenditures, excluding acquisitions and Real Estate and Related Assets).

The company is involved in the environmental investigation or remediation of numerous sites. Some of the sites are on property presently or formerly owned by the company where the company has the sole obligation to remediate the site or shares that obligation with one or more parties; others are third-party sites involving several parties who have a joint and several obligation to remediate the site; and some are superfund sites where the company has been named as a potentially responsible party. The company’s liability with respect to these sites ranges from insignificant at some sites to substantial at others, depending on the quantity, toxicity and nature of materials deposited by the company at the site and, with respect to some sites, the number and economic viability of the other responsible parties.

The company spent approximately $10 million in 2004, and expects to spend approximately $18 million in 2005, on environmental remediation of these sites. It is the company’s policy to accrue for environmental remediation costs when it is determined that it is probable that such an obligation exists and the amount of the obligation can be reasonably estimated. Based on currently available information, the company believes that it is reasonably possible that costs associated with all identified sites may exceed current accruals of $38 million by amounts that may prove insignificant or that could range, in the aggregate, up to approximately $60 million over several years. This estimate of the upper end of the range of reasonably possible additional costs is much less certain than the estimates upon which accruals are currently based and utilizes assumptions less favorable to the company among the range of reasonably possible outcomes.

The United States Environmental Protection Agency (U.S. EPA) has promulgated regulations dealing with air emissions from pulp and paper manufacturing facilities, including regulations on hazardous air pollutants that require use of maximum achievable control technology (MACT) and controls for pollutants that contribute to smog and haze. The final Cluster Rule package of regulations affecting the Pulp and Paper segment of the industry went into effect in 1998. The U.S. EPA has also adopted MACT standards for air emissions from wood products facilities and industrial boilers. The company anticipates that it might spend as much as $64 million over the next several years to comply with the MACT standards, including the Cluster Rules. The company cannot quantify future capital requirements needed to comply with new

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regulations being developed by the U.S. EPA or Canadian environmental agencies because final rules have not been promulgated. However, the company does not anticipate at this time that compliance with the new regulations will result in capital expenditures in any year that are material in relation to the company’s annual capital expenditures.

The American Forest & Paper Association has made a commitment on behalf of all members of the association to reduce greenhouse gas emissions intensity by 2012. The company also is actively participating in negotiations between the Forest Products Association of Canada and Natural Resources Canada to define industry obligations for complying with Canada’s national plan for reducing greenhouse gas emissions over the next several years. The company cannot estimate what expenditures may ultimately be required to contribute to these commitments but does not expect significant expenditures in 2005. During 2004, the company continued its work with international, national and regional policy makers in their efforts to develop technically sound and economically viable policies, practices and procedures for measuring, reporting and managing greenhouse gas emissions.

The U.S. EPA has repealed the regulations promulgated in 2000 that would have required states to develop total maximum daily load (TMDL) allocations for pollutants in water bodies determined to be water-quality-impaired. However, states continue to promulgate TMDL requirements. The state TMDL requirements may set limits on pollutants that may be discharged to a body of water or set additional requirements, such as best management practices for nonpoint sources, including timberland operations, to reduce the amounts of pollutants. It is not possible to estimate the capital expenditures that may be required for the company to meet pollution allocations across the various proposed state TMDL programs until a specific TMDL is promulgated.

PROPERTIES

TIMBERLANDS

Timberlands annual fee depletion, which reflects the acquisition of Willamette Industries (Willamette) in February 2002, follows:

WOOD PRODUCTS

Production capacities, facilities and annual production, which reflect the acquisition of Willamette in February 2002, are summarized by major product as follows:

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Principal manufacturing facilities are located as follows:

Lumber, plywood and veneer

Alabama, Arkansas, Louisiana, Mississippi, North Carolina, Oklahoma, Oregon, Washington; Alberta, British Columbia, Ontario and Saskatchewan, Canada

Composite panels

Arkansas, Louisiana, Oregon and South Carolina

Oriented strand board

Louisiana, Michigan, North Carolina, West Virginia; Alberta, New Brunswick, Ontario and Saskatchewan, Canada

Engineered lumber

Alabama, California, Georgia, Kentucky, Louisiana, Minnesota, Ohio, Oregon, West Virginia; Alberta, British Columbia and Ontario, Canada; and New South Wales, Australia

Hardwood lumber

Michigan, Oklahoma, Oregon, Washington, Wisconsin; and British Columbia, Canada

PULP AND PAPER

Production capacities, facilities and annual production, which reflect the acquisition of Willamette in February 2002, are summarized by major product as follows:

Principal manufacturing facilities are located as follows:

Pulp

Georgia, Kentucky, Mississippi, North Carolina, South Carolina and Washington; Alberta, British Columbia, Ontario and Saskatchewan, Canada

Paper

Kentucky, North Carolina, Pennsylvania, South Carolina, Tennessee, and Wisconsin; Ontario and Saskatchewan, Canada

Coated groundwood

Mississippi

Liquid packaging board

Washington

Paper converting

California, Indiana, Kentucky, North Carolina, Ohio, Pennsylvania, South Carolina, Tennessee, Texas, and Wisconsin; Ontario and Saskatchewan, Canada

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CONTAINERBOARD, PACKAGING AND RECYCLING

Production capacities, facilities and annual production, which reflect the acquisition of Willamette in February 2002, are summarized by major product as follows:

Principal manufacturing facilities are located as follows:

Containerboard

Alabama, California, Iowa, Kentucky, Louisiana, North Carolina, Oklahoma and Oregon; Xalapa, Mexico

Packaging

Alabama, Arizona, Arkansas, California, Colorado, Florida, Georgia, Hawaii, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maryland, Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Jersey, New York, North Carolina, Ohio, Oklahoma, Oregon, Tennessee, Texas, Virginia, Washington and Wisconsin; Guanajuato, Ixtac, Mexico City and Monterrey, Mexico

Specialty packaging

California, Georgia, Illinois, Indiana, Kentucky, North Carolina, Ohio and Oregon

Recycling

Arizona, California, Colorado, Illinois, Iowa, Kansas, Maryland, Minnesota, Nebraska, North Carolina, Oregon, Tennessee, Texas, Utah, Virginia and Washington

Kraft bags and sacks

California, Missouri, Oregon, and Texas

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REAL ESTATE AND RELATED ASSETS

Real estate operations are located as follows:

Single-family housing

California, Maryland, Nevada, Texas, Virginia and Washington

Residential land development

California, Maryland, Nevada, Texas, Virginia and Washington

Commercial and retail land development

California, Texas and Washington

Commercial projects

California

Real estate investments

Arizona, California, Colorado, Florida, Idaho, Illinois, Maryland, Nevada, Oregon, Utah, Virginia and Washington

LEGAL PROCEEDINGS

See “Management’s Discussion and Analysis of Financial Condition and Results of Operations” and Note 14 of Notes to Financial Statements in “Financial Statements and Supplementary Data” below for a summary of legal proceedings.

SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS

There were no matters submitted to a vote of security holders during the fourth quarter of the fiscal year ended December 26, 2004.

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MARKET PRICE FOR REGISTRANT’S COMMON EQUITY, RELATED STOCKHOLDER MATTERS AND ISSUER PURCHASES OF EQUITY SECURITIES

The company’s common stock trades on the following exchanges under the symbol WY: New York Stock Exchange, Chicago Stock Exchange and Pacific Stock Exchange. Exchangeable shares of the company trade on the Toronto Stock Exchange under the symbol WYL. At December 26, 2004, there were approximately 12,819 holders of record of common shares and 1,320 holders of record of exchangeable shares of the company. Dividends per share data and the range of closing market prices for the company’s common stock for each of the four quarters in 2004 and 2003 are included in Note 25 of Notes to Financial Statements in “Financial Statements and Supplementary Data” below.

On May 5, 2004, the company issued 16,675,000 common shares and received net proceeds from the offering, after deduction of the underwriting discount and other transaction costs, of $954 million.

Following is information about securities authorized for issuance under the company’s equity compensation plans:

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SELECTED FINANCIAL DATA

Dollar amounts in millions, except per-share figures