EXHIBIT 32.1

                            CERTIFICATION PURSUANT TO
                             18 U.S.C. SECTION 1350,
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

     This certification is provided pursuant to Section 906 of the
Sarbanes-Oxley Act of 2002, 18 U.S.C. Section 1350, and accompanies the annual
report on Form 10-K for the year ended December 31, 2005 (the "Form 10-K") of
Mercantile Bank Corporation (the "Issuer").

     I, Gerald R. Johnson, Jr., Chairman and Chief Executive Officer of the
Issuer, certify that:

     (i)  the Form 10-K fully complies with the requirements of Section 13(a) or
          Section 15(d) of the Securities Exchange Act of 1934 (15 U.S.C. 78m(a)
          or 78o(d)); and

     (ii) the information contained in the Form 10-K fairly presents, in all
          material respects, the financial condition and results of operations
          of the Issuer.

Dated: February 23, 2006


                                        /s/ Gerald R. Johnson, Jr.
                                        ----------------------------------------
                                        Gerald R. Johnson, Jr.
                                        Chairman and Chief Executive Officer