Yu Kimura, who lost his WBC lightweight title in March, is retiring from boxing.
The 32-year-old, who fought professionally while continuing to hold down a job with a trading company, revealed his intent to call it quits on his blog on Sunday. Kimura won the WBC world title last November in a decision over Mexico's Pedro Guevara.
In March, however, Kimura failed in his first title defense, losing a decision to Mexico's Ganigan Lopez.
"I'm done with boxing," Kimura wrote. "The time I spent doing it was invaluable."
The Chiba native was 18-3 with one draw and three knockouts during his career.