The robbery happened on Thursday night in the 4900 block of Baltimore Avenue.
Police say the suspect was seen casing the location about 10 minutes before he struck.
He walked in, pointed a gun at the cashier, then walked behind the counter and grabbed cash out of the drawer.
No one was hurt.
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.