The two men, one carrying a knife, hit the shop on the Albertbridge Road shortly before 10.40 pm.
They threatened staff before making off with a quantity of cigarettes and a sum of cash.
The masked men are described as wearing tracksuits and hooded tops with the hoods pulled up.
Detectives are now appealing for witnesses to the armed robbery.
DI Michelle Griffin said: “I am appealing for anyone who can help identify those involved in this incident or anyone who may be able to assist the investigation in any other way to contact my team in Musgrave Police Station on the non-emergency number 101.
“Or if someone would prefer to provide information about this crime without leaving their name they can do so via the Crimestoppers charity by calling 0800 555 111.”