It happened Tuesday afternoon at Cruz Family Grocery on the 1800 block of South 22nd Street.
Surveillance video captured the unknown male suspect walking into the store at 2:30 p.m.
He walks around the store and noticed the employees in the rear of the store were busy helping other customers.
Click here to watch the surveillance video
The suspect then walks back to the front of the store and pulls a handgun on the 49-year-old employee behind the counter.
The thief got away with an unknown amount of cash from the registers before fleeing the store heading west on the 2200 block of Mifflin Street.
There were no injuries reported during the robbery.
Police describe the suspect as a black male, 30 to 35-years-old with a heavy build. He was wearing a gray hooded sweatshirt, black pants, and armed with a handgun.
Anyone with information is asked to call police at 215.686.TIPS (8477) or text a tip to PPD TIP (773847).