Police officers attended the Jet service station on Manthorpe Road, Grantham, after receiving a report at 19:54pm last night of a robbery at the premises.
An investigation has begun into the second reported robbery at the service station in a week, after a first incident on 20 February.
Enquiries are underway as to whether the incidents are linked.
It is believed at this stage that an amount of money and cigarettes were taken from the premises.
Detective Sergeant Simon Mason, CID Grantham, said: “We are looking for help in identifying the offender for this crime. If you saw anything last night that you feel may be related in the area around Manthorpe Road between 7pm and 9pm, or if you have any other information relating to this incident please contact us as soon as possible.
We are asking for anyone who hasn’t spoken to officers already and witnessed the incident to contact us on 101 quoting incident 415 of 26 February.
Alternatively you can contact us through the independent charity Crimestoppers anonymously on 0800 555 111 or on-line at crimestoppers-uk.org.