The robbery happened at 10:09 a.m. Monday at the Police and Fire Credit Union at 7604 City Avenue.
The man allegedly handed the teller a threatening note and got away with cash.
The suspect is described as a black male, about 30 years old, standing 6'2" tall with a thin build. He was wearing a red checkered long sleeve shirt and a red cap.
Anyone with information is asked to contact Philadelphia Police at 215-686-TIPS (8477), text a tip to PPD TIP (773847) or through PhillyPolice.com.