[LETTERHEAD OF PRYOR, CASHMAN, SHERMAN & FLYNN APPEARS HERE]


                                                                     Exhibit 5.1

                                        January 16, 1998



Mack-Cali Realty Corporation
11 Commerce Drive
Cranford, New Jersey  07016

Gentlemen:

     We refer to the Registration Statement on Form S-8, (the "Registration
Statement"), to be filed by you with the Securities and Exchange Commission with
respect to the registration under the Securities Act of 1933, as amended (the
"Act"), of 2,400,000 shares (the "Shares"), $.01 par value per Share, of the
Common Stock of Mack-Cali Realty Corporation (the "Company"), for delivery under
the Company's Employee Stock Option Plan and the Director Stock Option Plan
(collectively, the "Plans").

     We are qualified to practice law in the State of New York.  We express no
opinion as to, and, for the purposes of the opinion set forth herein, we have
conducted no investigation of, and do not purport to be experts on, any laws
other than the laws of the State of New York, the Maryland General Corporation
Law and the federal laws of the United States of America.

     We have examined such documents as we considered necessary for the purposes
of this opinion. Based on such examination, it is our opinion that the Shares
have been duly authorized, and, upon issuance, will be legally issued, fully-
paid and non-assessable under the laws of the State of Maryland (the state of
incorporation of the Company).

     We consent to the use of this opinion as an exhibit to the Registration
Statement.

                                 Very truly yours,

                                 PRYOR, CASHMAN, SHERMAN & FLYNN