The fire broke out at about 3:30 AM on the first floor of a three-story converted row home on the 900 block of Federal Street.
When firefighters arrived they were told a that a woman on the first floor was trapped
inside.They battled through flames and smoke to rescue her.
She is in critical condition at Jefferson Hospital with third-degree burns.
It took firefighters about 20 minutes to gain control of the blaze.
The building has five units but only two of them were occupied. The other resident, a man on the second floor, managed to get out safely.
PECO is restoring power to neighboring homes that lost it during the fire.
Investigators are trying to determine if a gas leak sparked the blaze.