A man burst into a shop in Pontnewydd with a kitchen knife and demanded money from the terrified woman assistant.
The man, who wore a black scarf over his face, got away with a quantity of cash in the robbery at Richmond Stores, Richmond Road.
The man is described as being in his early 30s, balding, about five feet ten inches tall and of stocky build. He was wearing blue jeans, black hooded top and black gloves.
The woman who was threatened with the knife was shaken but uninjured in the robbery which happened at about 5pm on Wednesday (13).
The robber is believed to have left via Russell Street, New Street and then into the park off Brooklands Terrace.
If anyone has information or may have seen anything suspicious they are asked to call Gwent Police on 101 or call Crimestoppers on 0800 555111.