Nadezhda Tolokonnikova was transferred to a hospital in the Siberian town of Krasnoyarsk in mid-November following two hunger strikes she staged to protest at purported treatment in jail, a penitentiary official told RIA Novosti.
She is to be released in March.
In August 2012, a Moscow court sentenced Tolokonnikova and two other Pussy Riot members to two years in prison on hooliganism charges for performing a "punk prayer" protest against President Vladimir Putin in a Moscow cathedral.
Tolokonnikova went on a hunger strike in September, claiming she was forced to work 17-hour days and was denied rest on the weekends at the prison camp in Mordovia. She also complained of work-related injuries and abuse by prison guards.
Officials denied that Tolokonnikova was mistreated, RIA Novosti said.
Tolokonnikova ended her first hunger strike after nine days but resumed it in October. Several days later prison authorities said she would be moved to another prison.
RIA Novosti said friends and relatives were kept unaware of Tolokonnikova's whereabouts for nearly a month.