As filed with the Securities and Exchange Commission on April 6, 2017

Registration No. 333-            

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

CATALYST BIOSCIENCES, INC.

(Exact name of Registrant as specified in its charter)

260 Littlefield Avenue

South San Francisco, California 94080

(650) 266-8674

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

Nassim Usman, Ph.D.

Chief Executive Officer

Catalyst Biosciences, Inc.

South San Francisco, California 94080

(650) 266-8674

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

Copies to:

Stephen B. Thau

Alfredo B. D. Silva

Morrison & Foerster LLP

755 Page Mill Road

Palo Alto, CA 94304

(650) 813-5600

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 of 1933, 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.  ☒ 333-216663

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.  ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

CALCULATION OF REGISTRATION FEE

This Registration Statement shall become effective upon filing in accordance with Rule 462(b) under the Securities Act of 1933, as amended.

EXPLANATORY NOTE

This Registration Statement is being filed pursuant to Rule 462(b) as promulgated under the Securities Act of 1933, as amended, and includes the registration statement facing page, this page, the signature page, an exhibit index and the required opinion and consents solely to register (i) an additional $2,100,000 in Class A Units, with each Class A Unit consisting of one share of the Company’s common stock, par value $0.001 per share (the “Common Stock”), and a warrant to purchase half of one share of Common Stock, (ii) an additional $1,350,000 in Class B Units, with each Class B Unit consisting of one share of the Company’s Series A convertible preferred stock, par value $0.001 per share (the “Series A Preferred Stock”) and a warrant to purchase a number of shares of Common Stock equal to $1,000 divided by the conversion price of the Series A Preferred Stock, (iii) shares of Common Stock issuable upon conversion of the additional shares of Series A Preferred Stock and (iv) shares of Common Stock issuable upon exercise of the warrants issued under the additional Class A Units and Class B Units. The contents of the Registration Statement on Form S-1 (Registration No. 333-216663), as amended, including the exhibits and power of attorney thereto, which was declared effective by the Securities and Exchange Commission on April 6, 2017, are incorporated by reference in this Registration Statement.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, as amended, the Registrant has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized in the City of South San Francisco, State of California, on April 6, 2017.

SIGNATURES AND POWER OF ATTORNEY

Pursuant to the requirements of the Securities Act of 1933, as amended, this Registration Statement on Form S-1 has been signed by the following persons in the capacities and on the dates indicated.

EXHIBIT INDEX