<PAGE>   1

                                   FORM 10-K/A
                                (AMENDMENT NO. 1)

                UNITED STATES SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
(Mark One)

[X]  ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
     EXCHANGE ACT OF 1934
     FOR THE FISCAL YEAR ENDED DECEMBER 31, 1999

                                       OR

[ ]  TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
     EXCHANGE ACT OF 1934



                         Commission File No. 333-2522-01

                  SUN COMMUNITIES OPERATING LIMITED PARTNERSHIP
             (Exact name of registrant as specified in its charter)

STATE OF MICHIGAN                                                     38-3144240
State of Organization                                   I.R.S. Employer I.D. No.

                              31700 MIDDLEBELT ROAD
                                    SUITE 145
                        FARMINGTON HILLS, MICHIGAN 48334
                                 (248) 932-3100
          (Address of principal executive offices and telephone number)


           Securities Registered Pursuant to Section 12(b) of the Act:
                                      NONE

           Securities Registered Pursuant to Section 12(g) of the Act:
                                      NONE

         Indicate by check mark if disclosure of delinquent filers pursuant to
Item 405 of Regulation S-K is not contained herein, and will not be contained,
to the best of Registrant's knowledge, in definitive proxy or information
statements incorporated by reference in Part III of this Form 10-K or any
amendment to this Form 10-K.

                                      [ X ]

         Indicate by check mark whether the Registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
Registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days.

                                 X  Yes      No
                                ---      ---

         As of March 6, 2000, the aggregate market value of the Registrant's
partnership units held by non-affiliates of the Registrant was approximately
$142,000,000 based on the closing sales price of Sun Communities, Inc. (into
which the partnership units are convertible on a one-for-one basis) on such date
using beneficial ownership of stock rules adopted pursuant to Section 13 of the
Securities Exchange Act of 1934 to exclude partnership units owned by directors
and officers of Sun Communities, Inc., some of whom may not be held to be
affiliates upon judicial determination.




<PAGE>   2


                                    PART III

         The General Partner is the sole general partner of the Company and,
therefore, the information required by ITEMS 10, 11, 12 and 13 is included in
the General Partner's Form 10-K/A for the fiscal year ended December 31, 1999,
and is incorporated herein by reference.



                                   SIGNATURES

         Pursuant to the requirements of Section 13 or 15(d) of the Securities
Exchange Act of 1934, the registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.

Date:  April 28, 2000

                                   SUN COMMUNITIES OPERATING LIMITED
                                   PARTNERSHIP

                                   By:  Sun Communities, Inc., General Partner

                                        By:      /s/ Gary A. Shiffman
                                            -----------------------------------
                                                 Gary A. Shiffman, President