United States securities and exchange commission logo





                           July 16, 2020

       Scott Braunstein, M.D.
       President and Chief Executive Officer
       Marinus Pharmaceuticals, Inc.
       5 Radnor Corporate Center, Suite 500
       100 Matsonford Rd
       Radnor, PA 19087

                                                        Re: Marinus
Pharmaceuticals, Inc.
                                                            Registration
Statement on Form S-3
                                                            Filed July 9, 2020
                                                            File No. 333-239780

       Dear Dr. Braunstein:

              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 Jeffrey
Gabor at 202-551-2544 with any questions.




                           Sincerely,


                           Division of Corporation Finance

                           Office of Life Sciences
       cc:                                              Steven J. Abrams, Esq.