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As filed with the Securities and Exchange Commission on January 18, 2006

Registration No. 333-128250

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Pre-Effective

Amendment No. 4

to

FORM S-1

REGISTRATION STATEMENT

UNDER THE SECURITIES ACT OF 1933

KOPPERS HOLDINGS INC.

(Exact name of registrant as specified in its charter)

436 Seventh Avenue

Pittsburgh, Pennsylvania 15219

Telephone: (412) 227-2001

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Steven R. Lacy, Esq.

Senior Vice President, Administration, General Counsel and Secretary

Koppers Holdings Inc.

436 Seventh Avenue

Pittsburgh, Pennsylvania 15219

Telephone: (412) 227-2001

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies of communications to:

Approximate date of commencement of proposed sale to the public:    As soon as practicable after the effective date of this registration statement.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act, check the following box.  ¨

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ¨

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ¨

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.  ¨

If delivery of the prospectus is expected to be made pursuant to Rule 434, please check the following box.  ¨

CALCULATION OF REGISTRATION FEE

The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the registration statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

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The information in this prospectus is not complete and may be changed. We and the selling shareholders may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED JANUARY 18, 2006

10,000,000 Shares

Koppers Holdings Inc.

Common Stock

We are selling 8,700,000 shares of common stock and the selling shareholders are selling 1,300,000 shares of common stock. We will not receive any of the proceeds from the shares of common stock sold by the selling shareholders.

Prior to this offering, there has been no public market for our common stock. The initial public offering price of the common stock is expected to be between $14.00 and $16.00 per share. We have applied to list our common stock on the New York Stock Exchange under the symbol “KOP.”

The underwriters have an option to purchase a maximum of 1,500,000 additional shares from the selling shareholders to cover over-allotments of shares. We will not receive any of the proceeds from the shares of common stock sold by the selling shareholders pursuant to the underwriter’s over-allotment option.

Investing in our common stock involves risks. See “ Risk Factors” on page 12.

Delivery of the shares of common stock will be made on or about                     , 2006.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is                     , 2006.

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You should rely only on the information contained in this document or to which we have referred you. We have not authorized anyone to provide you with information that is different. This document may only be used where it is legal to sell these securities. The information in this document may only be accurate on the date of this document.

Dealer Prospectus Delivery Obligation

Until             , 2006 all dealers that effect transactions in these securities, whether or not participating in this offering, may be required to deliver a prospectus. This is in addition to the dealer’s obligation to deliver a prospectus when acting as an underwriter and with respect to unsold allotments or subscriptions.

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SUMMARY

You should read the following summary together with the more detailed information appearing elsewhere in this prospectus and the financial statements and other information included in this prospectus. In this prospectus, unless otherwise indicated or the context requires otherwise, when we use the terms the “Company,” “we,” “our” or “us,” we mean Koppers Inc., formerly known as Koppers Industries, Inc., and its subsidiaries on a consolidated basis for periods up until November 18, 2004 and Koppers Holdings Inc., or Koppers Holdings (formerly known as KI Holdings Inc.), and its subsidiaries on a consolidated basis for periods from and including November 18, 2004, when Koppers Holdings became the parent of Koppers Inc. The use of these terms is not intended to imply that Koppers Holdings and Koppers Inc. are not separate and distinct legal entities.

Our Company

We are a leading integrated global provider of carbon compounds and commercial wood treatment products. Our products are used in a variety of niche applications in a diverse range of end-markets, including the aluminum, railroad, specialty chemical, utility, rubber and steel industries. We provide products which represent only a small portion of our customers’ costs but are essential inputs into the products they produce and the services they provide. In the aggregate, we believe that we maintain the number one market position by volume in a majority of our principal product lines in North America, Australia and Europe.

We serve our customers through a comprehensive global manufacturing and distribution network, including 35 manufacturing facilities located in North America, Australasia, China, Europe and South Africa. We conduct business in 73 countries with over 2,600 customers, many of which are leading companies in their respective industries, including Alcoa Inc., CSX Transportation, Inc., Union Pacific Railroad Company, Norfolk Southern Corporation and Burlington Northern Santa Fe Railway. We believe that our customers place significant value on our industry-leading “Koppers” brand, which for more than 70 years has maintained a reputation for quality, reliability and customer service. For the twelve months ended September 30, 2005, we generated net sales of $999.7 million, net income of $10.8 million and EBITDA of $103.7 million. For information relating to our net sales, net income and EBITDA for the last three fiscal years, see “—Summary Historical Consolidated Financial Data” and for a reconciliation of EBITDA to net income, see footnote (6) under “—Summary Historical Consolidated Financial Data.”

We operate two principal businesses, Carbon Materials & Chemicals and Railroad & Utility Products. Through our Carbon Materials & Chemicals business (58% of 2004 net sales), we believe we are the largest distiller of coal tar in North America, Australia, the United Kingdom and Scandinavia. We process coal tar into a variety of products, including carbon pitch, creosote and phthalic anhydride, which are critical intermediate materials in the production of aluminum, the pressure treatment of wood and the production of plasticizers and specialty chemicals, respectively. Through our Railroad & Utility Products business (42% of 2004 net sales), we are the largest North American supplier of railroad crossties. Our other commercial wood treatment products include the provision of utility poles to the electric and telephone utility industries.

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The following charts provide a breakdown of our 2004 net sales by product and industry:

Industry Overview

We believe that demand for aluminum and railroad track maintenance substantially drive demand in our two principal businesses. According to the King Report, worldwide aluminum production increased 6.5% to 29.8 million metric tons in 2004 and is expected to grow by 7.6% in 2005 and 6.8% in 2006. Carbon pitch requirements for the aluminum industry were 2.8 million metric tons in 2004 and are expected to grow as a function of growth in aluminum production. Recent global restructuring in the electrode and aluminum markets has resulted in reduced consumption volumes of carbon pitch in domestic markets. Any prolonged decline in demand for aluminum or further restructuring in the electrode and aluminum markets could negatively impact our business.

The railroad crosstie business is benefiting from positive general economic conditions in the railroad industry and from expected increases in spending on both new track and existing track maintenance. A decline in maintenance spending by the seven largest railroads in North America, which we refer to as the Class 1 railroads, could negatively impact demand for our products. The Railway Tie Association, or RTA, estimates that approximately 13.7 million crossties for the Class 1 railroads were installed in the United States in 2004 and approximately 14.0 million crossties are projected to be installed in 2005. The RTA projects demand to increase by 9.2% to 15.3 million crossties in 2006. In addition, on August 10, 2005, a federal transportation bill was signed into law which provides $286.5 billion of funding for various projects in the transportation industry. Although it is difficult to estimate the impact of this legislation on our business, we believe that it is likely to benefit us directly by increased sales related to projects identified in the legislation or indirectly as additional railroad capital can be reallocated to infrastructure maintenance priorities.

For more information on our industry and recent trends, see “Business—Industry Overview.”

Key Competitive Strengths

We believe that we are distinguished by the following key competitive strengths:

Leading Market Positions Across Business Segments.    We are a leading integrated global provider of carbon compounds and commercial wood treatment products.

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The following table sets forth our leading market position for each of our principal product lines in our three major geographic regions:

Strong Customer Relationships Under Contract Arrangements.    Our reputation and industry-leading “Koppers” brand have enabled us to establish strong relationships with leading companies in their respective industries. All of our top ten customers are served under long-term contracts and approximately 56% of our 2004 net sales were made to customers with whom we have contract arrangements of two or more years.

Diverse End-Markets and Global Presence.    Our approximately 2,600 customers operate in diverse end-markets such as aluminum, railroads, specialty chemicals, including polyester resins, paints, coatings and plasticizers, steel, utilities, rubber, wood preservation, roofing and pavement sealers. We believe our global presence and our strategically located facilities enable us to capitalize on opportunities to increase sales of our existing product portfolio into higher-growth emerging economies, such as China, the Middle East, India and Eastern Europe.

Cost Advantage Through Vertical Integration.    The degree of vertical integration in our business enables us to utilize products produced in our Carbon Materials & Chemicals business in our manufacturing processes, providing us with significant cost and supply advantages. In addition, internally generated products provide a more reliable source of feedstock for our wood treatment and phthalic anhydride products.

Experienced and Incentivized Management Team.    Our senior management team has an average of 27 years of industry experience. Prior to the offering, our directors, management team and employees beneficially own approximately 24% of our equity.

For further information on our strengths, see “Business—Key Competitive Strengths.”

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Our Business Strategy

The key elements of our strategy are:

Capitalize on Attractive Growth Opportunities.    We believe our existing key end-markets, especially the aluminum and railroad industries, and geographic focus provide attractive growth opportunities. We are well positioned to capitalize on these opportunities. In addition, we intend to pursue growth opportunities in three ways:

Maximize Cash Flow and Reduce Financial Leverage.    We expect to reduce our financial leverage by using a portion of our net proceeds from this offering and a portion of cash flow from operations after required capital expenditures.

Continue Productivity and Cost Reduction Initiatives.    We are focused on improving our profitability and cash flows by achieving productivity enhancements and by improving our cost platform.

For further information on our business strategy, see “Business—Our Strategy.”

Risks Related to our Competitive Strengths and Business Strategy

The key competitive strengths that currently distinguish our company as well as the key elements of our business strategy are each subject to certain risks. Such risks include:

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Any of the above risks could adversely affect our financial position and results of operations. For additional risks related to our business or this offering, see “Risk Factors.”

Recent Developments

On August 8, 2005, the President signed the Energy Policy Act of 2005 into law. Included in this legislation are Section 29 Energy Tax Credits earned for the production and sale of coke to a third party. These credits against federal income tax will be earned in conjunction with the coke operations at our Monessen, Pennsylvania facility. The tax credit generated per ton of coke sold is tied to a per barrel of oil equivalent on a BTU basis and adjusted annually for inflation. The credits are effective January 2006, expire December 2009 and can be carried forward for 20 years. Based on our understanding of the legislation and subject to final determination of an oil price range, we could earn up to $4.0 million per year of credits that will reduce federal income taxes.

Principal Shareholder

Saratoga Partners III, L.P. has informed us that it is a New York based investment firm managed by Saratoga Management Company LLC making private equity investments in partnership with management in the business services and manufacturing industries. Saratoga Partners was founded in 1984 as the corporate buyout group of Dillon, Read & Co. Inc. and has been independent since 1998. Saratoga Partners is an experienced firm, having led buyout investments in 33 companies.

Corporate Information

We are a Pennsylvania corporation. Our principal offices are located at 436 Seventh Avenue, Pittsburgh, Pennsylvania 15219-1800. Our telephone number is (412) 227-2001. We maintain a website at www.koppers.com. The information contained on or linked to from our website does not constitute a part of this prospectus and is not incorporated by reference herein.

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The Offering

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The calculation of shares of common stock to be outstanding after this offering as presented here and throughout this prospectus, unless otherwise indicated, is based on 12,014,192 shares of our common stock outstanding immediately prior to the consummation of this offering and:

Risk Factors

Before making an investment in our common stock, you should consider carefully the information included in the “Risk Factors” section beginning on page 12 of this prospectus, as well as any other information contained in this prospectus.

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Summary Historical Consolidated Financial Data

The following table contains our summary historical consolidated financial data for the three years ended December 31, 2004 and as of and for the nine months ended September 30, 2005 and 2004 and the twelve months ended September 30, 2005. The summary historical consolidated financial data for each of the years ended December 31, 2004, 2003 and 2002 have been derived from our audited consolidated financial statements. The summary historical consolidated financial data as of and for the nine months ended September 30, 2005 and 2004 have been derived from our unaudited consolidated financial statements, which were prepared on the same basis as our audited consolidated financial statements and, in our opinion, reflect all adjustments, consisting only of normal recurring adjustments, necessary to fairly present our results of operations and financial condition for such periods. The summary historical consolidated financial data for the twelve months ended September 30, 2005 have been derived by adding our historical consolidated financial data for the year ended December 31, 2004 to our unaudited consolidated financial data for the nine months ended September 30, 2005 and subtracting our unaudited consolidated financial data for the nine months ended September 30, 2004. This is only a summary and should be read in conjunction with our historical consolidated financial statements and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” included elsewhere in this prospectus.