Longtime UCare chief Nancy Feldman said Wednesday that she will retire from the state's fourth-largest insurance company in June 2015.

Feldman has led the organization since 1995, and helped direct its growth from a small demonstration project in Hennepin County to a health plan that recently hit a milestone with 400,000 enrollees in Minnesota and western Wisconsin.

Feldman, 67, said it's a good time to take this "bittersweet" step, when the organization is strong.

"The world is changing," she said. "There's so much talk of alignments and mergers and who's doing what with whom. It seems to me that now's the time for someone to come into an organization of this size and look at that future."

UCare said its board of directors will conduct a national search for Feldman's replacement.

Feldman has led UCare on an unprecedented growth spurt in recent years, after winning additional state contracts through a new competitive-bidding process. It grabbed market share from much larger competitors Blue Cross and Blue Shield of Minnesota and Medica.

The explosive growth has boosted UCare's workforce to more than 600 employees, with offices stretched across three buildings around its longtime base in northeast Minneapolis.

Feldman took over the organization about a decade after its founding by a group of family doctors at the University of Minnesota, who sought stable insurance coverage for their poorest patients.

Until this year, UCare's entire book of business came from insuring low-income Minnesotans and seniors eligible for Medicare. The health plan branched into the private market this year by offering insurance policies for individuals shopping on MNsure, the state's new insurance exchange.

In addition to reading books, ­biking and traveling, Feldman said retirement will free up more time for her to advocate for a fund she quietly started with the War Legacies Project in memory of her husband.

Bob Feldman died in 2006 of complications from exposure to Agent Orange while serving in the Vietnam War. His fund builds homes and provides services for Vietnamese families still affected by the herbicide, which was sprayed on jungles across Southeast Asia by American planes during the war.