The victim is a 12-year-old boy who suffered from autism, according to authorities.
The fire in the 100 block of South 55th Street started just before 7 p.m.
Firefighters report that in the 30 minutes before the flames were brought under control, the fire started at 137 South 55th Street, then spread to 135, 139 and 141.
The cause of the fire is under investigation.
At least one official of Firefighters Union Local 22 is blaming the recent fire brownouts for the fataility.
Action News spoke with Philadelphia Fire Commissioner Lloyd Ayers, who said the city's new brownout policy did not have any affect on the response to Saturday night's fire.
Last week, the city of Philadelphia started a "brownout" policy of closing some fire companies on a rotating basis. The firefighters at the companies that are closed are then sent for training or to fill in for other firefighters who have called out sick at other companies.
For more information, click these links:
Philadelphia Fire Department Memorandum
Local 22 of the Fire Fighters Union to the Philadelphia City Council