Hospital officials said Rebozo died before 11 p.m. EDT at Baptist Hospital. They would not disclose the cause of death or any other details.
The Miami Herald reported Saturday that doctors said Rebozo died of a brain aneurysm and that Rebozo had suffered complications from a stroke.
Rebozo's sister, Mary Bouterse, said Rebozo had family members with him when he died.
Rebozo had been in "pretty good health" recently but was hospitalized for four days before his death, she said from her Miami home. Bouterse said she did not know why her brother was hospitalized.
Rebozo, a gas station owner who became a millionaire banker, was the longtime president and chairman of Key Biscayne Bank. He and Nixon were neighbors in Key Biscayne, and the president visited Rebozo in Florida frequently while he was in office.
It was during one such visit in June 1972 when Nixon first learned of the break-in at the Democratic Party headquarters that would eventually force him to resign in disgrace two years later.
"We were swimming at Key Biscayne in front of my house," Rebozo told The Miami Herald in a 1990 interview. "They came out and told him. He said, 'What in God's name were they doing there'?"
Then, Rebozo said, "We laughed and forgot about it."
On June 17, 1972, five men hired by the White House were arrested in the Democratic Party headquarters in the Watergate Office Building.
Dismissed by the White House at the time as "a third-rate burglary," it proved devastating to the president, who approved steps to divert an FBI investigation.
Rebozo was at the president's side the night he decided to quit the presidency, and Nixon resigned on Aug. 9, 1974.
Nixon, named by a federal grand jury as one of 18 unindicted co-conspirators, received "a full, free and absolute pardon" from his successor, President Gerald Ford.
In the two years following the break-in, Nixon frequently consulted with Rebozo. The two remained friends after Nixon left office, with the former president continuing his visits to Florida from his home in Yorba Linda, Calif. Nixon died in 1994.
Rebozo called Watergate a "terrible experience." But seeing Nixon weather the crisis helped him, he said in the 1990 interview.
"The truth of the matter is, I don't think I could have taken it had I not seen what he was taking, and how he was surviving," said Rebozo, who also was investigated during the Watergate scandal.
Rebozo shunned the spotlight after the turbulent Watergate years. He once was asked whether he would discuss the success of the Key Biscayne Bank, Rebozo replied: "No, thank you. I've had all of the publicity I ever ant."
Survivors include Rebozo's wife, Jane Lucke Rebozo, and his sister.