The discovery on Saturday raises the number of deaths to at least 12.
Coast Guard Cmdr. Cosimo Nicastro said the body, wearing a life jacket, was found in a narrow corridor near an evacuation staging point at the ship's rear.
The body was brought to Giglio, the Tuscan island where the cruise liner hit a reef and ran aground on Jan. 14. Twenty people are missing.
Meantime, officials said a small amount of fuel has leaked into the sea surrounding the ship. The spill reportedly came from machines on the ship, not its tanks, which hold nearly a half-million gallons of fuel.
The Associated Press contributed to this report.