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


     Each of the undersigned, Martin A. White, the Chairman of the
Board and Chief Executive Officer, and Warren L. Robinson, the
Executive Vice President and Chief Financial Officer of MDU Resources
Group, Inc. (the "Company"), DOES HEREBY CERTIFY that:

     1.  The Company's Quarterly Report on Form 10-Q for the quarter
ended June 30, 2005 (the "Report") fully complies with the
requirements of Section 13(a) of the Securities Exchange Act of 1934;
and

     2.  Information contained in the Report fairly presents, in all
material respects, the financial condition and results of operation
of the Company.

     IN WITNESS WHEREOF, each of the undersigned has executed this
statement this 3rd day of August, 2005.


                               /s/ Martin A. White
                              Martin A. White
                              Chairman of the Board and
                              Chief Executive Officer



                               /s/ Warren L. Robinson
                              Warren L. Robinson
                              Executive Vice President and
                              Chief Financial Officer



A signed original of this written statement required by Section 906
has been provided to MDU Resources Group, Inc. and will be retained
by MDU Resources Group, Inc. and furnished to the Securities and
Exchange Commission or its staff upon request.