EXHIBIT 5.1

               [LETTERHEAD OF PRYOR CASHMAN SHERMAN & FLYNN LLP]

                                              June 4, 1999

Mack-Cali Realty Corporation
11 Commerce Drive
Cranford, New Jersey 07016
Ladies and Gentlemen:

    We are acting as counsel to Mack-Cali Realty Corporation, a Maryland
corporation (the "Company"), in connection with the Registration Statement on
Form S-8, File No. 333-      (the "Registration Statement"), as filed by the
Company with the Securities and Exchange Commission with respect to the
registration under the Securities Act of 1933, as amended (the "Act"), of
580,000 shares (the "Shares") of the common stock, par value $0.01 per share, of
the Company for delivery under the Company's Deferred Compensation Plan for
Directors (the "Plan").

    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 securities 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 in accordance with the Plan, will
be legally issued, fully-paid and non-assessable under the laws of the State of
Maryland.

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

    This opinion is furnished in connection with the transactions covered
hereby. This opinion may not be relied upon by you for any other purpose, or
furnished to, quoted to, or relied upon by any other person, firm or corporation
for any purpose, without our prior written consent.

                                          Very truly yours,
                                          /s/ Pryor Cashman Sherman & Flynn LLP