Shinsuke Yamanaka, ranked No. 1 in the WBC bantamweight division, lost Thursday's rematch against Luis Nery of Mexico in a second-round TKO at Tokyo's Ryogoku Kokugikan.
The fight came a day after Nery was stripped of the bantamweight title after failing to make weight.
Yamanaka, who failed to retake the WBC title, afterward expressed his intention to retire.
The bantamweight title will be vacant. Yamanaka lost his title defense to Nery in August last year on a fourth-round TKO. It was later discovered Nery tested positive for a muscle-building banned substance, and the WBC ordered the rematch.
In another title match on Thursday, IBF super bantamweight champion Ryosuke Iwasa defended his belt for the first time with a unanimous decision over 13th-ranked Ernest Saulong of the Philippines.
In the locker room after the match, the 35-year old Yamanaka wore an expression of relief while speaking about his future.
"This is the last one. This is the end," said Yamanaka, who had at one stretch defended the bantamweight title 12 consecutive times.
The match started with booing toward Nery because of his failure to make weight. Yamanaka wasn't bad at the start, delivering jabs and guarding himself well, based on knowledge gained from their first match.
But toward the end of the first round, Nery caught him with a right-hand counter, knocking Yamanaka off balance. The Japanese boxer did not go down, but that punch disrupted his footwork, and Nery knocked him to the canvas just before the end of the first.
In the second, it was no match. Yamanaka went down three times and ended the bout on the canvas. Yamanaka was irked by Nery's failure to make weight as well as the Mexican's doping issue.
"At the weigh-in, I couldn't stop feeling irritated," Yamanaka said. The first time Nery weighed in, he was as heavy as a featherweight -- two divisions above bantamweight.
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