The incident happened on June 25 just before 6:00 p.m. at the the Makiman Sushi Restaurant on the 7300 block of Oxford Avenue.
The robber was caught on surveillance walking into the restaurant the back entrance and covering his face with a t-shirt.
He approaches the counter, pulls out a large knife and demanded money.
Click here to see the surveillance video
The employee can be seen backing away as the suspect grabs cash from the register.
He got away with an unknown amount of money before fleeing the scene, possibly in a gray Nissan with some front end damage.
Police describe the suspect as a male of unknown race, late 20-30 years-of-age with a medium build. He was wearing a black shirt, black jeans, and a black shirt covering his face.
If you see this suspect, do not approach him and call 911 immediately.
Anyone with information should call police at 215.686.TIPS (8477) or text a tip to PPD TIP (773847).