Miami Fire Rescue found the 42-year-old man dehydrated but alive on a homemade raft made of four inner tubes strapped together, the Miami Herald reported Monday.
He told the U.S. Coast Guard three other men were missing and "he feared the others had drowned," said Ignatius Carroll, a spokesman for Miami Fire Rescue.
The survivor was rushed to an area hospital.
The body of one rafter was found not far from the raft and taken to the Miami-Dade Medical Examiner, Coast Guard Petty Officer Mark Barney said.
The search for the two missing rafters was expected to continue Tuesday.
Boaters alerted the Coast Guard to the survivor after spotting him about 3 p.m. about seven miles southwest of Key Biscayne.
Fire Rescue was the first to respond because their vessel was the closest to the raft, Barney said.
At least 271 Cubans have been intercepted in the Florida Straits since Oct. 1.