CERTIFICATION


I, Warren L. Robinson, certify that:

  1. I have reviewed this quarterly report on Form 10-Q of
     MDU Resources Group, Inc.;

  2. Based on my knowledge, this report does not contain any
     untrue statement of a material fact or omit to state a
     material fact necessary to make the statements made, in
     light of the circumstances under which such statements
     were made, not misleading with respect to the period
     covered by this report;

  3. Based on my knowledge, the financial statements, and
     other financial information included in this report,
     fairly present in all material respects the financial
     condition, results of operations and cash flows of the
     registrant as of, and for, the periods presented in
     this report;

  4. The registrant's other certifying officer and I are
     responsible for establishing and maintaining disclosure
     controls and procedures (as defined in Exchange Act
     Rules 13a-15(e) and 15d-15(e)) and internal control
     over financial reporting (as defined in Exchange Act
     Rules 13a-15(f) and 15d-15(f)) for the registrant and
     have:

       (a) Designed such disclosure controls and
           procedures, or caused such disclosure controls and
           procedures to be designed under our supervision, to
           ensure that material information relating to the
           registrant, including its consolidated subsidiaries,
           is made known to us by others within those entities,
           particularly during the period in which this report
           is being prepared;

       (b) Designed such internal control over financial
           reporting, or caused such internal control over
           financial reporting to be designed under our
           supervision, to provide reasonable assurance
           regarding the reliability of financial reporting and
           the preparation of financial statements for external
           purposes in accordance with generally accepted
           accounting principles;

       (c) Evaluated the effectiveness of the registrant's
           disclosure controls and procedures and presented in
           this report our conclusions about the effectiveness
           of the disclosure controls and procedures, as of the
           end of the period covered by this report based on
           such evaluation; and

       (d) Disclosed in this report any change in the
           registrant's internal control over financial
           reporting that occurred during the registrant's most
           recent fiscal quarter (the registrant's fourth
           fiscal quarter in the case of an annual report) that
           has materially affected, or is reasonably likely to
           materially affect, the registrant's internal control
           over financial reporting; and

  5. The registrant's other certifying officer and I have
     disclosed, based on our most recent evaluation of
     internal control over financial reporting, to the
     registrant's auditors and the audit committee of the
     registrant's board of directors (or persons performing
     the equivalent functions):

       (a) All significant deficiencies and material
           weaknesses in the design or operation of internal
           control over financial reporting which are
           reasonably likely to adversely affect the
           registrant's ability to record, process, summarize
           and report financial information; and

       (b) Any fraud, whether or not material, that
           involves management or other employees who have a
           significant role in the registrant's internal
           control over financial reporting.

Date:  August 3, 2005


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