OSAKA (Kyodo) Satoshi Ishii, the men's over-100-kg gold medalist at the Beijing Olympics, announced Monday his decision to quit judo and become a professional mixed martial artist.

"I'm starting a professional career today," Ishii said at a press conference in Osaka. "It's not easy to fight in mixed martial arts and I'm ready to start from step one with a white belt (for beginners)."

"I've got an impression that mixed martial arts have many of the strongest fighters (in all types of martial arts) and so I had already made up my mind to join them whatever the outcome would be at the Olympics."

Ishii, 21, is the third Japanese gold medalist in Olympic judo to join mixed martial arts, following the precedence of Hidehiko Yoshida and Makoto Takimoto. Yoshida won the 78-kg event at the 1992 Barcelona Games and Takimoto took the 81-kg gold in Sydney in 2000.