Certification Pursuant to Section 906 of the Sarbanes-Oxley Act

I, Gifford R. Zimmerman, Chief Administrative Officer of Nuveen Municipal Market
Opportunity Fund, Inc., certify that:

     1.   The Form N-CSR of the Fund (the "Report") fully complies with the
          requirements of Section 13(a) or 15(d) of the Securities Exchange Act
          of 1934; and

     2.   The information contained in the Report fairly presents, in all
          material respects, the financial condition and results of operations
          of the Fund.

A signed original of this written statement required by Section 906, or other
document authenticating, acknowledging, or otherwise adopting the signature that
appears in typed form within the electronic version of this written statement
required by Section 906, has been provided to Nuveen Municipal Market
Opportunity Fund, Inc. and will be retained by Nuveen Municipal Market
Opportunity Fund, Inc. and furnished to the Securities and Exchange Commission
or its staff upon request.


Date: July 8, 2003
      -----------------------

                                           /s/ Gifford R. Zimmerman
                                               ---------------------
                                               Chief Administrative Officer
                                               (chief executive officer)




Certification Pursuant to Section 906 of the Sarbanes-Oxley Act

I, Stephen D. Foy, Principal Financial Officer of Nuveen Municipal Market
Opportunity Fund, Inc., certify that:

     1.   The Form N-CSR of the Fund (the "Report") fully complies with the
          requirements of Section 13(a) or 15(d) of the Securities Exchange Act
          of 1934; and

     2.   The information contained in the Report fairly presents, in all
          material respects, the financial condition and results of operations
          of the Fund.

A signed original of this written statement required by Section 906, or other
document authenticating, acknowledging, or otherwise adopting the signature that
appears in typed form within the electronic version of this written statement
required by Section 906, has been provided to Nuveen Municipal Market
Opportunity Fund, Inc. and will be retained by Nuveen Municipal Market
Opportunity Fund, Inc. and furnished to the Securities and Exchange Commission
or its staff upon request.


Date: July 8, 2003
      -----------------------

                                           /s/ Stephen D. Foy
                                               ---------------------
                                               Vice President, Controller
                                               (Chief Financial Officer)