MDU Resources Increases Common Stock Dividend 6.55 Percent<br>

August 17, 2006

MDU Resources Increases Common Stock Dividend 6.55 Percent

Bismarck, ND

The Board of Directors of MDU Resources Group, Inc. (NYSE:MDU) at its regular meeting today declared a quarterly common stock dividend of 13.5 cents per share, a 6.55 percent increase from the previously stated split-adjusted quarterly dividend of 12.67 cents. This results in an annualized increase of 3.3 cents per share.

“We are pleased we’ve been able to increase our dividend every year for the past 16 years and have provided an unbroken record of consecutive dividend payments to our shareholders since 1937,” said Harry J. Pearce, chairman of MDU Resources. “Results for the first half of the year show the continuing strength of MDU Resources’ diversified business portfolio. The Board of Directors believes it is important to share the corporation’s success with the investors who have demonstrated their confidence in MDU Resources by purchasing stock.”

The diversified natural resource company’s Board of Directors also declared dividends on preferred stock as follows:
$1.12-1/2 per share on 4.50 percent Series Preferred
$1.17-1/2 per share on 4.70 percent Series Preferred
$1.27-1/2 per share on 5.10 percent Series Preferred
The dividends are payable Oct. 1, 2006, to stockholders of record Sept. 14, 2006.

MDU Resources Group, Inc., a member of the S&P MidCap 400 index, provides value-added natural resource products and related services that are essential to energy and transportation infrastructure. MDU Resources includes natural gas and oil production, construction materials and mining, domestic and international independent power production, natural gas pipelines and energy services, electric and natural gas utilities, and construction services. For more information about MDU Resources, see the company’s Web site at www.mdu.com or contact the Investor Relations Department at investor@mduresources.com.

Contacts:

   Financial:

     Daryl Splichal
     Senior Assistant Treasurer
     (701) 530-1019

     Phyllis Rittenbach
     Director of Investor Relations
     (701) 530-1057

   Media:

     Linda Donlin
     Director of Communications and Public Relations
     (701) 530-1700