Two men, one holding what appeared to be a gold-coloured gun, robbed the KFC in Turnells Mill Lane, Wellingborough.
The robbery happened at about 1.30am on Saturday, November 16, when two men entered the restaurant.
One of the men was carrying what appeared to be a handgun and the other was carrying a knife.
The offenders told staff to open the safe and stole a quantity of cash.
They ran off towards Tesco and The Embankment.
One of the offenders was white, 5ft 6in to 5ft 8in, and of medium build.
He was wearing dark clothing and blue rubber gloves.
His lower face was covered with a scarf and he was carrying a gold-coloured gun.
The second offender was black, about 6ft, large and stocky.
He was wearing dark jogging bottoms, a dark hooded top and black gloves.
His lower face was also covered with a scarf.
A small white van was seen in the area shortly before the robbery.
Witnesses to this incident, or anyone with information, should call Northamptonshire Police on 101 or anonymously to Crimestoppers on 0800 555 111.