Niagara Mohawk Power Corp., a subsidiary of National Grid plc (NYSE: NGG), announced that its Board of Directors has declared dividends at the following rates for all series of its preferred stock.

.85% of $100 par value, 3.40% Series;

.90% of $100 par value, 3.60% Series;

.975% of $100 par value, 3.90% Series.

Preferred stock dividends are payable on June 30, 2011, to holders of record on June 7, 2011; ex-dividend date June 3, 2011.

Niagara Mohawk Power Corp., doing business as National Grid, provides electricity service to approximately 1.5 million customers and natural gas service to approximately 565,000 customers in upstate New York. The company is based in Syracuse, N.Y. Its parent company National Grid plc is an international energy delivery company. In the U.S., National Grid delivers electricity to approximately 3.3 million customers in Massachusetts, New Hampshire, New York and Rhode Island, and manages the electricity network on Long Island under an agreement with the Long Island Power Authority (LIPA). It is the largest distributor of natural gas in the northeastern U.S., serving approximately 3.4 million customers in Massachusetts, New Hampshire, New York and Rhode Island. National Grid also owns over 4,000 megawatts of contracted electricity generation that provides power to over one million LIPA customers.

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