The body was found on the third deck where some of the 114,500-tonne vessel's lifeboats were located, with rescuers declining to give further details.
Emergency workers had pulled the bodies of two women from the wreck on Monday, saying that they were found near the luxury liner's Internet cafe.
Italian Maria D'Introno, 30, identified late Monday, was on the cruise with her husband and in-laws, who were celebrating their 50th wedding anniversary, and they were just settling down for dinner when the accident happened.
Too scared to throw herself into the sea along with the others despite having a life jacket, D'Introno stayed on the sinking ship as it keeled over after running aground on January 13.
Other victims include Hungarian Sandor Feher, 42, who helped children into a lifeboat before heading back towards his cabin to get his violin, and Frenchman Francis Servel, 71, who gave his wife his lifejacket. She survived.
Crews from Dutch company Smit Salvage on the Tuscan island of Giglio meanwhile were looking for the best way to access the Costa Concordia's 23 fuel tanks before syphoning the oil out of the ship beached on the rocky shoreline.
"The company's divers will carry out underwater operations which will probably take two days," said Claudio Chiavacci, who is coordinating joint operations by salvage workers and rescuers searching for missing people.
The Costa Concordia went down on January 13 with 4,229 people on board. It emerged Tuesday that Italian prosecutors were looking into the cruise ship operator's possible role in the wreck and reports of a chaotic evacuation.
"The employer is the guarantor and is responsible. We have to look at the choices made by the operator," Beniamino Deidda, chief prosecutor for the region where the disaster occurred, was quoted by Italian media as saying.
"For now the attention has been on the fault of the captain, who turned out to be tragically incompetent. But who chooses the captain?" Deidda said.
Captain Francesco Schettino is under house arrest, accused of manslaughter, causing a shipwreck and abandoning ship.
The prosecutor also pointed to multiple problems with the evacuation, including a lack of preparation for the emergency among crew members.
While navy divers blew a new hole in the ship on the third deck to aid rescuers searching for 16 people still missing after the crash, a large pontoon with a barge attached could be seen operating near the vessel.
The head of Italy's civil protection agency, Franco Gabrielli, said the salvage workers were likely to begin syphoning off the oil by Saturday, and would start by emptying six large tanks holding half of the ship's oil.
The coastguard has said that emptying the fuel tanks will take weeks.
Smit will carry out a so-called "hot-tapping" operation, which involves pumping the fuel out into a nearby ship and replacing it with water so as not to affect the ship's balance and stop it from slipping into the open sea.
The race is now on to empty the ship's fuel tanks, as environmentalists warn that an oil spill would be a catastrophe in Europe's biggest marine sanctuary.
Rescuers on Monday said a slick measuring 60,000 square metres had already appeared.
"The slick is made up of hydrocarbons, it is a very fine film, so fine it cannot be collected mechanically but can only be absorbed. It seems to be wash from inside the ship," Gabrielli said.
Hundreds of metres of absorbent barriers have been put down around the wreck to contain any possible oil spills. Gabrielli said there has also been some contamination of the sea from toxic substances on board.
Gabrielli said emergency workers would continue to search for missing people while others tried to clear out the wreckage. Decomposition of food, furniture clutter and the turbid waters were complicating the work, he said.