It is hoped the examination will establish the sex of the body, how the person died and if it is father-of-two Richard Davies who went missing while on a Christmas works night.
Police divers had been searching the River Taff for nearly a month after Richard Davies, 39, from Blaenavon, disappeared on 20 December.
The body was recovered from the water 150m downstream from the Penarth Road bridge in Cardiff city centre.
Dental records may be needed to establish the identity of the body.
It is believed it has been in the water for some time.
Posters
Mr Davies' wife Michelle has been informed of the find by family liaison officers, which is standard procedure in situations such as these.
Mr Davies was last seen by friends in St Mary Street shortly before 2300 GMT on their night out.
He had spent the morning go-karting in Newport before he and colleagues caught the 1600 GMT train to Cardiff.
They drank in a number of city centre bars and pubs.
Mr Davies was wearing navy trousers and a light blue shirt and was last seen in a bar called Reflex.
At the time of the disappearance, there were separate reports that a man was seen in the River Taff near the Millennium Stadium.
Michelle Davies, the missing man's wife, later circulated leaflets and posters across the city in an effort to find fresh information about her husband.
Mr Davies's disappearance was described as being completely out of character.
The couple have two children, Justin, 13, and Charlotte, 10.
~RS~a~RS~International~RS~q~RS~~RS~z~RS~54~RS~)