Jiang Weiping was released Tuesday after the one year remaining on his sentence was commuted, and he was with his family in the northeastern city of Dalian, said John Kamm, executive director of the Duihua Foundation in San Francisco. Kamm said he had spoken to Jiang's wife.
Kamm said he didn't know the reason for the early release.
But Hu is due to visit the United States early this year, and Beijing frequently releases prominent prisoners in connection with high-level official contacts with the United States.
"It could be related to preparations for Hu Jintao's visit," Kamm said by telephone from San Francisco. "Certainly the U.S. has been saying some gestures are needed, because we haven't had any recently."
Jiang's name was on a list of prisoners cited in speeches by Clark T. Randt, the U.S. ambassador to Beijing. All of the others have been released, though China hasn't freed a prominent prisoner since its best-known Muslim activist, Rebiya Kadeer, was released in March 2005 and allowed to leave for the United States.
Jiang has bee detained since December of 2000, after he wrote a series of articles exposing government corruption for a Hong Kong magazine. Jiang was sentenced to nine years in prison following a secret trial held on September 5, 2001, according to the Committee to Protect Journalists.
A court later cut his sentence from eight to six years.
The governor, Bo Xilai, is now China's commerce minister.
Jiang was convicted under China's vague state secrets law, which has been used recently against other journalists.