Exhibit 24

                                POWER OF ATTORNEY

        KNOW ALL BY THESE PRESENTS, as of this 27th day of April, 2015, that the
undersigned hereby constitutes and appoints the Chief Executive Officer of Seres
Health, Inc. (the "Company"), who is currently Roger J. Pomerantz, and the Chief
Financial Officer of the Company who is currently Eric D. Shaff, or either of
them signing singly, and with full power of substitution, the undersigned's true
and lawful attorney-in-fact to:

     (1)  prepare, execute in the undersigned's name and on the undersigned's
          behalf, and submit to the U.S. Securities and Exchange Commission (the
          "SEC") a Form ID, including amendments thereto, and any other
          documents necessary or appropriate to obtain codes and passwords
          enabling the undersigned to make electronic filings with the SEC of
          reports required by Section 16(a) of the Securities Exchange Act of
          1934 or any rule or regulation of the SEC;

     (2)  execute for and on behalf of the undersigned, in the undersigned's
          capacity as an officer and/or director of Seres Health, Inc. (the
          "Company"), Forms 3, 4, and 5 in accordance with Section 16(a) of the
          Securities Exchange Act of 1934 and the rules thereunder;

     (3)  do and perform any and all acts for and on behalf of the undersigned
          which may be necessary or desirable to complete and execute any such
          Form 3, 4, or 5, complete and execute any amendment or amendments
          thereto, and timely file such form with the SEC and any stock exchange
          or similar authority; and

     (4)  take any other action of any type whatsoever in connection with the
          foregoing which, in the opinion of such attorney-in-fact, may be of
          benefit to, in the best interest of, or legally required by, the
          undersigned, it being understood that the documents executed by such
          attorney-in-fact on behalf of the undersigned pursuant to this Power
          of Attorney shall be in such form and shall contain such terms and
          conditions as such attorney-in-fact may approve in such
          attorney-in-fact's discretion.

        The undersigned hereby grants to each such attorney-in-fact full power
and authority to do and perform any and every act and thing whatsoever
requisite, necessary, or proper to be done in the exercise of any of the rights
and powers herein granted, as fully to for me to fix your for all intents and
purposes as the undersigned might or could do if personally present, with full
power of substitution or revocation, hereby ratifying and confirming all that
such attorney-in-fact, or such attorney-in-fact's substitute or substitutes,
shall lawfully do or cause to be done by virtue of this power of attorney and
the rights and powers herein granted. The undersigned acknowledges that the
foregoing attorneys-in-fact, in serving in such capacity at the request of the
undersigned, are not assuming, nor is the Company assuming, any of the
undersigned's responsibilities to comply with Section 16 of the Securities
Exchange Act of 1934.

        This Power of Attorney shall remain in full force and effect until the
undersigned is no longer required to file Forms 3, 4, and 5 with respect to the
undersigned's holdings of and transactions in securities issued by the Company,
unless earlier revoked by the undersigned in a signed writing delivered to the
foregoing attorneys-in-fact.

        IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to
be executed as of the date first written above.

                                        /s/ Roger J. Pomerantz
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                                        Signature

                                        Roger J. Pomerantz
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                                        Printed Name