The robbery happened at 10:04 a.m. at the First Trust Bank branch at 1931 Cottman Avenue.
Investigators say the suspect entered the bank and gave a teller a demand note. He told the teller he had a gun, though no weapon was displayed.
After obtaining an undisclosed amount of cash, the man fled the bank on foot.
The suspect is described as a white male in his mid to late 20's, 6'0" tall, thin build, with brown hair, wearing a red "Phillies" baseball cap, and a red t-shirt with a red long sleeve shirt underneath.
Anyone with information is asked to call the Philadelphia Police Department, or the FBI at 215-418-4000.
There may be a reward for information leading to the man's capture, and tipsters can remain anonymous.