United States securities and exchange commission logo July 28, 2021 Aiofe M. Brennen, MB,BCh,BAO,MMSc Chief Executive Officer Synlogic, Inc. 301 Binney St., Suite 402 Cambridge, Massachusetts 02142 Re: Synlogic, Inc. Registration Statement on Form S-3d Filed July 23, 2021 File No. 333-258151 Dear Dr. Brennen: This is to advise you that we have not reviewed and will not review your registration statement. Please refer to Rules 460 and 461 regarding requests for acceleration. We remind you that the company and its management are responsible for the accuracy and adequacy of their disclosures, notwithstanding any review, comments, action or absence of action by the staff. Please contact Abby Adams at (202) 551-6902 with any questions. Sincerely, Division of Corporation Finance Office of Life Sciences cc: Daniel Bagliebter, Esq.