UNITED STATES SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549


                                   FORM 10-K/A
                                (Amendment No. 1)


     [X]        ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF
                       THE SECURITIES EXCHANGE ACT OF 1934

                   For the fiscal year ended December 31, 2006

                                       OR

     [ ]      TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF
                       THE SECURITIES EXCHANGE ACT OF 1934

         For the transition period from _____________ to ______________

                          Commission file number 1-3480

                            MDU Resources Group, Inc.
             (Exact name of registrant as specified in its charter)

      Delaware                                         41-0423660
 (State or other jurisdiction of                    (I.R.S. Employer
  incorporation or organization)                    Identification No.)

                            1200 West Century Avenue
                                  P.O. Box 5650
                        Bismarck, North Dakota 58506-5650
                    (Address of principal executive offices)
                                   (Zip Code)

                          (701) 530-1000 (Registrant's
                     telephone number, including area code)


Securities registered pursuant to Section 12(b) of the Act:

                                                   Name of each exchange
             Title of each class                    on which registered
             -------------------                    -------------------
        Common Stock, par value $1.00             New York Stock Exchange
    and Preference Share Purchase Rights



Securities registered pursuant to Section 12(g) of the Act:

                         Preferred Stock, par value $100
                         -------------------------------
                                (Title of Class)

Indicate by check mark if the registrant is a well-known seasoned issuer, as
defined in Rule 405 of the Securities Act. Yes |X| No | |

Indicate by check mark if the registrant is not required to file reports
pursuant to Section 13 or Section 15(d) of the Exchange Act. Yes | | No |X|

Indicate by check mark whether the registrant (1) has filed all reports required
to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during
the preceding 12 months (or for such shorter period that the registrant was
required to file such reports), and (2) has been subject to such filing
requirements for the past 90 days. Yes |X| No | |

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405
of Regulation S-K is not contained herein, and will not be contained, to the
best of the registrant's knowledge, in definitive proxy or information
statements incorporated by reference in Part III of this Form 10-K or any
amendment to this Form 10-K. |X|

Indicate by check mark whether the registrant is a large accelerated filer, an
accelerated filer, or a non-accelerated filer. See definition of "accelerated
filer and large accelerated filer" in Rule 12b-2 of the Exchange Act (Check
one):

Large accelerated filer |X|  Accelerated filer | |  Non-accelerated filer | |

Indicate by check mark whether the registrant is a shell company (as defined in
Rule 12b-2 of the Act). Yes | | No |X|

State the aggregate market value of the voting common stock held by
nonaffiliates of the registrant as of June 30, 2006: $4,393,239,107.

Indicate the number of shares outstanding of each of the registrant's classes of
common stock, as of February 12, 2007: 181,147,966 shares.

DOCUMENTS INCORPORATED BY REFERENCE
Portions of the registrant's 2007 Proxy Statement are incorporated by reference
in Part III, Items 10, 11, 12, 13 and 14 of this Report.





                                Explanatory Note

The information contained in Items 10, 11 and 13 in the Annual Report on Form
10-K filed on February 21, 2007 did not incorporate by reference all required
information from the Company's 2007 Proxy Statement.


                                    PART III

ITEM 10.  DIRECTORS, EXECUTIVE OFFICERS AND CORPORATE GOVERNANCE

The information required by this item is included under the captions "Item 1.
Election of Directors," "Continuing Incumbent Directors," "Information
Concerning Executive Officers," the first and third paragraphs under "Corporate
Governance - Audit Committee," "Corporate Governance - Code of Conduct" and
"Section 16(a) Beneficial Ownership Reporting Compliance" in the Proxy
Statement, which information is incorporated herein by reference.

ITEM 11. EXECUTIVE COMPENSATION

The information required by this item is included under the caption "Executive
Compensation" in the Proxy Statement, which information is incorporated herein
by reference.

ITEM 13. CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS, AND DIRECTOR
INDEPENDENCE

The information required by this item is included under the captions "Related
Person Disclosure" and "Corporate Governance - Director Independence" in the
Proxy Statement, which information is incorporated herein by reference.

                                     PART IV

ITEM 15. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES

(a)     FINANCIAL STATEMENTS, FINANCIAL STATEMENT SCHEDULES AND EXHIBITS

3.  Exhibits

Exhibits filed herewith:

31(a)     Certification of Chief Executive Officer filed pursuant to Section 302
          of the Sarbanes-Oxley Act of 2002

31(b)     Certification of Chief Financial Officer filed pursuant to Section 302
          of the Sarbanes-Oxley Act of 2002

                                       1


32        Certification of Chief Executive Officer and Chief Financial Officer
          furnished pursuant to 18 U.S.C. Section 1350, as adopted pursuant to
          Section 906 of the Sarbanes-Oxley Act of 2002

                                       2



                                   SIGNATURES

Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange
Act of 1934, the registrant has duly caused this amendment to be signed on its
behalf by the undersigned, thereunto duly authorized.

                                             MDU RESOURCES GROUP, INC.

Date:  March 1, 2007                         By: /s/ Vernon A. Raile
                                                 -------------------
                                                 Vernon A. Raile
                                                 Executive Vice President,
                                                 Treasurer and Chief Financial
                                                 Officer

                                       3




                                  EXHIBIT INDEX

Exhibit Number      Description of Exhibit

31(a)               Certification of Chief Executive Officer filed pursuant to
                    Section 302 of the Sarbanes-Oxley Act of 2002

31(b)               Certification of Chief Financial Officer filed pursuant to
                    Section 302 of the Sarbanes-Oxley Act of 2002

32                  Certification of Chief Executive Officer and Chief Financial
                    Officer furnished pursuant to 18 U.S.C. Section 1350, as
                    adopted pursuant to Section 906 of the Sarbanes-Oxley Act of
                    2002