The woman was at the fourth-floor level of the 102-year-old stadium and fell onto the roof of the elevator car at the second floor after a game between the Boston Red Sox and the Detroit Tigers, Boston Fire Department spokesman Steve MacDonald said.
Firefighters shut off power to the elevator and used a chair to climb through a hatch onto the roof of the elevator car to rescue the unconscious woman, MacDonald said.
The woman, whose identity was not released, was taken to the city's Beth Israel Deaconess Medical Center in serious condition, MacDonald said.