In June 1981, he won via a fifth-round knockout, in the undercard of Ayub Kalule vs. Sugar Ray Leonard, at the Reliant Astrodome, Houston.
Mihara knocked him down by his right cross in the fourth round, and won the title via a majority decision.
"[6] He lost his title after suffering a knockout during his first defence, against Davey Moore at the Tokyo Metropolitan Gymnasium on February 2, 1982.
[1] Following this loss, Mihara won the Japanese junior middleweight title and defended it six times until June 1984, then returned it.
[1] He fought for a final time in March 1985, beating Tricky Kawaguchi by a unanimous decision.