UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 OR 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): April 5, 2017

FibroGen, Inc.

(Exact name of registrant as specified in its charter)

FibroGen, Inc.

409 Illinois Street

San Francisco, CA 94158

(Address of principal executive offices, including zip code)

(415) 978-1200

(Registrant’s telephone number, including area code)

Not Applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Item 8.01. Other Events.

On April 5, 2017, FibroGen, Inc. (the “Registrant”) entered into an underwriting agreement with Leerink Partners LLC and Stifel, Nicolaus & Company, Incorporated, relating to the issuance and sale of 5,228,750 shares of the Registrant’s common stock (the “Offering”) at a price to the public of $22.95 per share. The gross proceeds to the Registrant from the Offering are expected to be $120.0 million before deducting the underwriting discounts and commissions and offering expenses payable by the Registrant. The offering is scheduled to close on or about April 11, 2017, subject to customary closing conditions.

The underwriting agreement contains customary representations, warranties, covenants and agreements by the Registrant, indemnification obligations of the Registrant and the underwriters, including for liabilities under the Securities Act of 1933, as amended, other obligations of the parties and termination provisions. The representations, warranties and covenants contained in the underwriting agreement were made only for purposes of such agreement and as of specific dates, were solely for the benefit of the parties to the underwriting agreement, and may be subject to limitations agreed upon by the contracting parties.

The Offering is being made by means of a written prospectus supplement and accompanying prospectus forming part of a shelf registration statement on Form S-3 (Registration Statement No. 333-216368), previously filed with the Securities and Exchange Commission (“SEC”) and declared effective by the SEC on March 1, 2017.

The underwriting agreement is attached as Exhibit 1.1 hereto, and the description of the terms of the underwriting agreement is qualified in its entirety by reference to such exhibit. A copy of the opinion of Cooley LLP relating to the legality of the issuance and sale of the shares in the Offering is attached as Exhibit 5.1 hereto.

On April 6, 2017, the Registrant issued a press release announcing the pricing of the Offering. A copy of this press release is attached as Exhibit 99.1 hereto.

Neither the disclosures on this Current Report on Form 8-K nor the attached press release shall constitute an offer to sell or the solicitation of an offer to buy these securities, nor shall there be any sale of these securities in any state or jurisdiction in which such an offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Date: April 6, 2017