The Hobbit Pub in Bevois Valley was broken into by a man searching for money on Tuesday.
The Cancer Research UK charity bucket situated at the bar was stolen after the man tried looking inside the empty till while staff were upstairs before opening. Staff claim that CCTV images show the break in took six minutes.
Security cameras at the pub show him climbing over the back fence near the Beer Garden at around 2:50pm before entering the building.
The man had dark hair and was wearing dark trousers with a light and dark blue striped top.
The bucket was allegedly found empty in the pub toilets but the bucket is thought to have contained around £30 in cash.
Anyone who recognises this man or with information on the incident should call Hampshire Police on 101.