Police say a man armed with a knife threatened two members of staff during the robbery at the Albertbridge Road petrol station in east Belfast around 9.25 pm on Sunday night.
The man went into the shop and threatened at knifepoint a man and woman working on the premises.
He then fled with a sum of cash.
No-one was injured in the incident.
The PSNI say the man is described as being in his early 20s, and was wearing a grey tracksuit with the hood up over his face.
Anyone who saw what happened or who has any further information has been asked to contact the police on the non-emergency number 101.