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                                                                     EXHIBIT 5.1

                              Dickinson Wright PLLC
                         500 Woodward Avenue, Suite 4000
                             Detroit, Michigan 48226
                             Phone No. 313-223-3500
                           Facsimile No. 313-223-3598


April 18, 2001

Securities and Exchange Commission
450 Fifth Street, N.W.
Washington, D.C 20549


   Re:   Mercantile Bank Corporation
         Registration Statement on Form S-3

Ladies and Gentlemen:

         We are acting as special counsel to Mercantile Bank Corporation, a
Michigan corporation (the "Company"), in connection with the filing with the
Securities and Exchange Commission of a Registration Statement on Form S-3 (the
"Registration Statement") relating to up to 446,600 shares of the Company's
common stock, without par value (the "Common Stock"). The Common Stock is being
offered for sale by certain shareholders of the Company who received the shares
in a private placement transaction. The Company is registering the shares to
enable the selling shareholders to resell the shares in the public market from
time to time or on a delayed basis.

         In connection with our opinion, we have examined originals, or copies,
certified or otherwise identified to our satisfaction, of the Registration
Statement, the Articles of Incorporation and the By-Laws of the Company, as well
as such other corporate records, documents and other papers as we deemed
necessary to examine for purposes of this opinion. We have assumed the
authenticity, accuracy and completeness of all documents submitted to us as
originals, the conformity to authentic original documents of all documents
submitted to us as certified, conformed or photostatic copies and the
genuineness of all signatures.

         Based on the foregoing, we are of the opinion that the 446,600 shares
of Common Stock offered pursuant to the Registration Statement have been legally
issued, and are fully paid and non-assessable shares.

         The opinion expressed herein is limited to the Federal securities laws
and the laws of the State of Michigan currently in effect.

         We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the use of our name under the heading "Legal
Matters" in the Prospectus included in the Registration Statement.

                                     Very truly yours,


                                     /s/ Dickinson Wright PLLC