It happened just before 1:00 p.m. in the 800 block of Cherry Street.
Rescuers say a man was trapped in the basement, but firefighters were able to get him out.
He was flown to the Hospital of the University of Pennsylvania in serious, but not life-threatening, condition.
The fire started in the rear of the building, investigators said, but no cause has been released.
The fire was quickly brought under control at 1:10pm.