The blaze broke out at about 12:45 Wednesday morning inside the Raim Ahuvim synagogue.
The building is on the 5800 block of Drexel Road in Wynnefield.
When firefighters arrived they saw flames spitting out of the windows on the second and third floors.
The fire quickly spread to the attic.
It took 45 minutes for firefighters to bring it under control.
There are no reports of injuries, but the building has suffered heavy smoke and fire damage.
Raim Ahuvim is an Orthodox congregation that holds prayer services twice a day.
