Exhibit 32.1

CERTIFICATIONS OF PRINCIPAL EXECUTIVE OFFICER AND PRINCIPAL FINANCIAL OFFICER

PURSUANT TO 18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO SECTION 906

OF THE SARBANES-OXLEY ACT OF 2002

In connection with the Annual Report on Form 10-K (the “Annual Report”) of 4D Molecular Therapeutics, Inc. (the “Company”) for the year ended December 31, 2021, David Kirn, as Chief Executive Officer of the Company, and August J. Moretti, as Chief Financial Officer of the Company, each hereby certify, pursuant to 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that, to the best of his knowledge:

a)the Company’s Annual Report for the year ended December 31, 2021 fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended; and

b)the information contained in such Annual Report fairly presents, in all material respects, the financial condition and results of operations of 4D Molecular Therapeutics, Inc.

Dated: March 28, 2022

By:	/s/ David Kirn
	David Kirn
	Chief Executive Officer
	(Principal Executive Officer)

Dated: March 28, 2022

By:	/s/ August J. Moretti
	August J. Moretti
	Chief Financial Officer
	(Principal Financial and Accounting Officer)