September 14, 2018

Jonathan P. Mow
Chief Executive Officer
PhaseBio Pharmaceuticals, Inc.
Regus Del Mar
12707 High Bluff Drive, Suite 200
San Diego, CA 92130

       Re: PhaseBio Pharmaceuticals, Inc.
           Amendment No. 1 to Draft Registration Statement on Form S-1
           Submitted August 31, 2018
           CIK No. 0001169245

Dear Mr. Mow:

     We have reviewed your amended registration statement and have the
following
comment.

       Please respond to this letter by amending your registration statement
and providing the
requested information. If you do not believe our comment applies to your facts
and
circumstances or do not believe an amendment is appropriate, please tell us why
in your
response.

       After reviewing any amendment to your registration statement and the
information you
provide in response to this comment, we may have additional comments. Unless we
note
otherwise, our references to prior comments are to comments in our August 24,
2018 letter.

Amendment No. 1 to Draft Registration Statement on Form S-1 submitted August
31, 2018

Prospectus Summary
Overview, page 1

1.     We note your revisions in response to our prior comment 2 and continue
to object to your
       characterization of PB2452 as "first-in-class." Adding the qualifier
"potentially" does not
       address our concerns that your product candidate is in the early stages
of development and
       has only been tested on healthy patients. Please remove this statement.
 Jonathan P. Mow
PhaseBio Pharmaceuticals, Inc.
September 14, 2018
Page 2

        You may contact Tabatha Mccullom at 202-551-3658 or Jim Rosenberg at
202-551-3679
if you have questions regarding comments on the financial statements and
related
matters. Please contact Irene Paik at 202-551-6553 or Mary Beth Breslin at
202-551-3625 with
any other questions.



                                                         Sincerely,
FirstName LastNameJonathan P. Mow
                                                         Division of
Corporation Finance
Comapany NamePhaseBio Pharmaceuticals, Inc.
                                                         Office of Healthcare &
Insurance
September 14, 2018 Page 2
cc:       Darren K. DeStefano - Cooley LLP
FirstName LastName