A cashier at Rushden Service Station was threatened with a knife when two men ran into the premises and stole a quantity of cash from behind the counter.
She was uninjured but extremely shaken by the incident, which happened on Sunday, 31 July at 10.20pm at the service station on Wellingborough Road.
Both offenders ran off into Wellingborough Road towards Windmill Road.
They are described as white and of medium build, about 5ft 9in and both wearing grey hoodies.
Anyone who witnessed the robbery or has any information regarding the incident can ring Northamptonshire Police on 101 and ask for Wellingborough CID, or contact Crimestoppers anonymously on 0800 111555.