Andrew Gestyn Richards, 52, was staying at an authorised address in Swansea, south Wales, after being released on temporary licence from HMP Leyhill in South Gloucestershire. However, he failed to return to the open Category D prison on Friday.
Richards had been serving time there since 1995, for offences including assault, indecent assault and rape, Wales Online reports.
Police suspect the rapist is now camping in south Wales and have warned the public not to approach him.
He has particular links to the Bridgend and Porthcawl areas.
A statement from Avon and Somerset Police said: “Officers believe he could be camping, possibly wild camping, and may have travelled from the Swansea area.”
Richards is described as white, clean shaven and about 5ft 10ins (1.78m) tall, with grey hair.
When last seen he was wearing a black baseball cap, grey jacket, black Adidas three-stripe shorts and blue trainers.
He was also carrying a dark-blue drawstring bag, a large black holdall and a rolled-up green item, possibly a tent.
If you see him, you should call 999 immediately.