The robbery happened at approximately 3pm yesterday, Wednesday September 1, at Greenfield Stores in Newbridge.
Two men, one armed with a knife, entered the shop premises and demanded money from a woman shop worker.
Both men are described as white, one had blonde hair and was wearing a grey hooded top with the hood. The other wearing a black hooded top with the hood up and also had a black holdall bag with him.
The two men made off with a substantial amount of money and cigarettes.
Enquiries are ongoing and anyone with any information is asked to call Gwent Police on 01633 838111 or Crimestoppers on 0800 555 111.