The U.N. High Commissioner for Refugees said in a news release fishermen had found the survivor off the Tunisian coast Monday night and alerted the Tunisian Coast Guard, which rescued the man.
The survivor, who had been floating on a fuel container and the remains of the boat, told UNHCR staff the boat had left Tripoli in late June and reached the Italian coast a day later but high winds forced it to return to sea.
The boat was punctured in the Mediterranean Sea within a few days and air started to leak out.
The survivor said there was no water on board and people began dying of dehydration within days. He and many others drank sea water.
He said more than half of those who died, including three of his relatives, were from Eritrea.
The survivor was taken to a hospital in Zarzis, Tunisia, for treatment of dehydration and exposure.
The UNHCR said more than 1,300 people have arrived by boat from Libya in Italy this year and about 170 people have been declared dead or lost at sea attempting to make the journey from Libya to Europe.
"I call upon all vessels at sea to be on heightened alert for migrants and refugees needing rescue in the Mediterranean," T. Alexander Aleinikoff, deputy high commissioner for refugees, said in the news release. "The Mediterranean is one of the busiest seaways in the world and it is imperative that the time-honored tradition of rescue at sea be upheld."