August 24, 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.
           Draft Registration Statement on Form S-1
           Submitted July 27, 2018
           CIK No. 0001169245

Dear Mr. Mow:

       We have reviewed your draft registration statement and have the
following comments. In
some of our comments, we may ask you to provide us with information so we may
better
understand your disclosure.

       Please respond to this letter by providing the requested information and
either submitting
an amended draft registration statement or publicly filing your registration
statement on
EDGAR. If you do not believe our comments apply to your facts and circumstances
or do not
believe an amendment is appropriate, please tell us why in your response.

      After reviewing the information you provide in response to these comments
and your
amended draft registration statement or filed registration statement, we may
have additional
comments.

Draft Registration Statement on Form S-1 submitted July 27, 2018

Prospectus Summary, page 1

1.     We note that you intend to pursue "accelerated approval" of PB2452 as a
ticagrelor
       reversal agent, if considered appropriate by the FDA. Please describe
the specific
       regulatory pathway for this approval and the basis under which such
approval may be
       granted.
 Jonathan P. Mow
FirstNamePharmaceuticals, Inc. Mow
PhaseBio LastNameJonathan P.
Comapany NamePhaseBio Pharmaceuticals, Inc.
August 24, 2018
August 24, 2018 Page 2
Page 2
FirstName LastName
2.       We note your statements here and in the Business section that your
lead product
         candidate is a first-in-class reversal agent. These statements imply
an expectation of
         regulatory approval and are inappropriate given the early stage of
development. Please
         remove or revise these statements.
Strategy, page 3

3.       Please revise your disclosure to provide context regarding your
statement on page 3 that
         you "retain worldwide commercial rights to PB2452 and PB1046" to
clarify that you
         license PB2452 from AstraZeneca and, to the extent true, the rights to
the ELP technology
         underlying PB1046 from Duke.
4.       Please revise the first and second bullet points to put into context
your statements
         concerning your intention and ability to "rapidly advance" PB2452 and
PB1046 through
         clinical trials. In this regard, we note your disclosure on page 15
which indicates that
         clinical product development involves a lengthy and expensive process,
with an uncertain
         outcome.
Implications of Being an Emerging Growth Company, page 5

5.       Please supplementally provide us with copies of all written
communications, as defined in
         Rule 405 under the Securities Act, that you, or anyone authorized to
do so on your behalf,
         present to potential investors in reliance on Section 5(d) of the
Securities Act, whether or
         not they retain copies of the communications.
Use of Proceeds, page 57

6.       Please revise this section to disclose the development stages you will
be able to reach for
         PB2452 and PB1046 with your existing cash and the net proceeds of this
offering. In
         addition, to the extent you will need to raise additional capital to
complete such stage of
         development, please disclose the amount and sources of such other
funds needed to
         complete such trials. Refer to Instruction 3 to Item 504 of Regulation
S-K.
Management's Discussion and Analysis of Financial Condition and Results of
Operations
Critical Accounting Policies and Significant Judgements and Estimates
Determination of the Fair Value of Common Stock, page 77

7.       Once you have an estimated offering price or range, please explain to
us how you
         determined the fair value of the common stock underlying your equity
issuances and the
         reasons for any differences between the recent valuations of your
common stock leading
         up to the IPO and the estimated offering price. This information will
help facilitate our
         review of your accounting for equity issuances including stock
compensation and
         beneficial conversion features.
 Jonathan P. Mow
PhaseBio Pharmaceuticals, Inc.
August 24, 2018
Page 3
Business
ELP Technology, page 95

8.    We note your disclosure that you have conducted clinical trials on
product candidates
      based on your ELP technology that you are no longer developing. Please
provide an
      explanation of why you decided to discontinue development of these
product candidates.
Index to Financial Statements
Notes to the Financial Statements
9. Redeemable Convertible Preferred Stock and Stockholders' Deficit
Conversion, page F-20

9.    You state, "All Preferred Stock, except the Series 2, is automatically
converted into
      common stock in the event of an initial public offering of specified
characteristics, or
      upon the agreement of 60% of the Preferred Stock, voting together as a
single class on an
      as-converted basis." Please disclose the specified characteristics
required for automatic
      conversion.
General

10.   Please provide us proofs of all graphic, visual, or photographic
information you will
      provide in the printed prospectus prior to its use, for example in a
preliminary prospectus.
      Please note that we may have comments regarding this material.
        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
August 24, 2018 Page 3
cc:       Darren K. DeStefano - Cooley LLP
FirstName LastName