Miyazaki amassed a 9–0–2 record before being booked to face the #9 ranked WBC light flyweight contender Munetsugu Kayo for the Japanese light-flyweight title on 12 October 2009.
[1] Miyazaki made his first title defense against the #1 ranked Japanese light flyweight contender Suguru Takizawa on 21 February 2010.
[2] Miyazaki challenged the #9 ranked WBC light flyweight contender Katsuhiko Iezumi for the OPBF light-flyweight title on 14 June 2010.
[6] Miyazaki made his fourth and final OPBF light flyweight title defense against Michael Landero on 20 June 2012, whom he beat by unanimous decision.
The vacant championship bout took place on the undercard of the Kazuto Ioka and José Alfredo Rodríguez light flyweight title fight.
The fight was scheduled as the co-main event of the Kazuto Ioka and Kwanthai Sithmorseng WBA light flyweight championship bout and took place at the same venue as his previous two appearances.
[20] His four-fight win streak earned Miyazaki the chance to challenge Ryoichi Taguchi for the WBA light-flyweight championship.
[24] In September 2017, Miyazaki was arrested for driving without a driver's license, which led to him being suspended by the Japanese boxing commission as well.
[26] Miyazaki faced Takayuki Teraji in a 51.5 kg catchweight bout on 16 December 2021, following a five-year absence from the sport, in the co-main event of 3150 Fight Club.