Doctors were scheduled to remove Choi's organs for transplantation Wednesday night after getting approval from the prosecutors' office.
"He has lived a hard life," South Korea's Yonhap news agency quoted Oh Soon-hui, Choi's 65-year-old mother, as saying.
"I hope he has gone to a peaceful place."
Critics of boxing have called for the sport to be banned, saying it can cause lasting brain damage and other injuries as well as death.
In 1982, South Korean lightweight Kim Duk-koo died four days after being knocked out by Ray "Boom Boom" Mancini in a WBA lightweight world title fight in Las Vegas.
Kim was knocked out in the 14th round, prompting the WBC to reduce the length of its bouts from 15 to 12 rounds – a move later followed by other major boxing bodies.
Another South Korean fighter, bantamweight Lee Tong-choon, died of acute swelling of the brain in 1995, four days after losing consciousness following a Japanese title fight against Setsuo Kawamasu in Tokyo.