Police say it happened around 1:33 a.m. at the BP Gas Station on 1760 Dual Highway.
Police say the masked man entered the store armed with a knife. They say the man fled on foot with an undisclosed amount of money and cigarettes.
Police say the suspect was wearing a gray hooded sweatshirt, a black stocking cap, and blue jeans.
The investigation is ongoing.
Anyone with information regarding this incident is asked to call the city of Hagerstown Police Department, Criminal Investigators Division at (301)-790-3700 ext 234.