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 Quarterly Report on Form 10-Q (the “Report”) of 4D Molecular Therapeutics, Inc. (the “Company”) for the period ended September 30, 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 Report for the period ended September 30, 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 Report fairly presents, in all material respects, the financial condition and results of operations of the Company.

Dated: November 10, 2021

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

Dated: November 10, 2021

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