Fidelity Investments added 522,000 defined contribution plan participants and $25.2 billion in assets under administration during the first half of this year, a 36% increase over the assets added in the first half of 2011.

Marking one of its strongest sales increases in the last five years, Fidelity added 838 defined contribution retirement clients in the first half of 2012.

New defined contribution plans signed so far this year include Fortune 500 companies such as Kraft Foods, which has 51,000 participants and $6.2 billion in assets. Fidelity also gained $2.5 billion in assets in the tax-exempt market, including the University of Washington's retirement program with 27,000 participants.

Fidelity added more than 450 new clients through advisor-sold 401(k) plans with nearly 100,000 participants and $2.6 billion in assets.

"The defined contribution market continues to be highly competitive," says Jeff Lagarce, executive vice president, workplace investing at Fidelity Investments. "Because retirement has always been at the core of Fidelity's business, we continue to make substantial investments in our defined contribution business ... with industry leading technology and robust guidance."

Fidelity has 15.7 million retirement plan participants. The company has a total of $3.6 trillion in asset under administration.