The victim was in the water off Bunker Bay, a popular tourist spot on Australia's west coast, when the shark attacked on Sunday, biting him so badly the lower half of his body was torn away, police said.
Local reports said a Great White Shark, up to 4.5 metres long (14.7 feet), was thought to be responsible, with a plane and boats scouring the coastline to find it with the beach remaining closed.
Sergeant Craig Anderson from Dunsborough police told reporters it was "perfect shark conditions".
"It was dark and gloomy water, overcast skies, light rain falling, there was whale action in the bay and some seals about," he said told by AFP.
It is the first fatal shark attack in the country since February, when a man diving for abalone was savaged off South Australia, and only the fourth since December 2008. All but one have been off the west coast.
Anderson said the dead man, who has not been named, was among a group of about five surfing in the area.
"You have to take your hat off to the young fellow who was surfing with him and his mate for bringing him ashore, the nature of his injuries were significant," he said.
Shark expert Hugh Edwards told the West Australian newspaper that the area, from Cape Naturaliste to Cape Leeuwin, was a "travel route" for sharks, particularly great whites.
"The risk of being attacked while in the water is very low but there's no doubt that there are far more people in the water in these areas than there were 10, 20 years ago so we are seeing more attacks," he said. (C003)