Issei Ishii

is a Japanese kickboxer and Muay Thai fighter. He is a former K-1 Bantamweight Champion and WBC Muay Thai world champion.

Martial arts career KNOCK OUT Ishii faced the one-time Lumpinee Stadium flyweight title challenger Kazuki Osaki for the inaugural KNOCK OUT Flyweight championship at KING OF KNOCK OUT 2018 on December 9, 2018. He won the fight by majority decision, with all three judges scoring the bout 49–48 in his favor.

Ishii faced Yoddoy Kaewsamrit for the WPMF World Flyweight championship in his next fight, at KODO 4 on February 24, 2019. He won the fight by a third-round technical knockout.

After capturing the KNOCK OUT and WPMF titles, Ishii fought Petchthailand Moopingaroijung for the vacant IBF Muay Thai World Flyweight title at the June 12, 2019 Suk Wan Kingthong event. He won the fight by a third-round knockout, stopping Petchthailand with a spinning backfist at the very end of the round. Petchthailand and Ishii fought an immediate rematch at the August 9, 2019 True4U event, with the WBC Muay Thai World Super Flyweight title on the line. Ishii lost the fight by decision, with scores of 48–49, 47–49 and 47–50.

Ishii faced Nuapetch KelaSport in a non-title bout at the November 13, 2019 Suk Wan Kingthong event. He won the fight by third-round technical knockout.

Battle of Muaythai Ishii was booked to face Hiroyuki for the Battle of Muay Thai Super Flyweight title at BOM WAVE 01 ~ Get Over The COVID-19 on June 28, 2020. He won the fight by unanimous decision, with two judges scoring the bout 49–47 in his favor, while the third judge scored the bout 50–47 in his favor.

Ishii faced Yuya Iwanami in a non-title bout at NO KICK NO LIFE ~Shin Shou~ Diamond FES on October 29, 2020. He won his promotional debut by a second-round technical knockout, after he forced Iwanami's corner to throw in the towel.

Ishii made his first BoM Super Flyweight title defense against Satoshi Katashima at BOM WAVE 01 ~ Get Over The COVID-19 on December 6, 2020. Aside from Ishii's title, the WPMF World Super Flyweight title was on the line as well. Ishii won the fight by unanimous decision, with scores of 50–46, 49–48 and 49–47.

Ishii faced Reiya in a non-title bout at NO KICK NO LIFE ~Shin Shou~ Ungaisouten on February 24, 2021. He won the fight by unanimous decision, with all three judges awarding him a 30–28 scorecard. Ishii faced Sanchai TeppenGym in another non-title bout at BOM WAVE 04 – Get Over The COVID-19 on April 11, 2021. He won the fight by a fourth-round knockout.

Ishii was booked to face Kazuki Osaki at RISE WORLD SERIES 2021 on July 18, 2021, in the semifinals of the 2021 RISE Dead or Alive super flyweight tournament. The winner of the tournament was expected to face Tenshin Nasukawa in his final bout with the promotion. Ishii lost his RISE debut by unanimous decision, with scores of 29-28, 29-28 and 29-27.

Ishii returned to Battle of Muaythai for his next fight, a non-title bout against Kojima Nor.Naksin at BOM WAVE 06 – Get Over The COVID-19 on November 7, 2021. He won the fight by unanimous decision, with all three judges scoring it 49–48 for Ishii.

On January 9, 2021 Ishii faced Ryu Hanaoka at the NO KICK NO LIFE event. He lost by unanimous decision after five rounds.

Ishii faced Khun Namisan Shobukai at BOM WAVE 08 – Get Over The COVID-19 on April 24, 2022, in his final fight with the promotion before signing with K-1. He won the fight by a second-round knockout.

K-1 On June 14, 2022, it was revealed that Ishii had signed with K-1. He was booked to make his promotional debut against Kazuki Fujita at K-1 World GP 2022 in Fukuoka on August 11, 2022. Ishii won the fight by a third-round knockout, flooring Fujita with a right straight at the 2:41 minute mark of the round.

Ishii faced Detchphet Wor.Sangprapai for the vacant WBC MuayThai World Super Flyweight title at The Battle of Muay Thai "OUROBOROS" on September 23, 2022. He won the fight by knockout in the first round with a series of left hooks.

Ishii faced the undefeated WKA World -54 kg champion Oscar Bohorquez in the quarterfinals of the 2022 K-1 Bantamweight World Grand Prix. The one-day tournament, held to crown the inaugural K-1 bantamweight champion, was held at K-1 World GP 2022 in Osaka on December 3, 2022. He forced a referee stoppage with a flurry of punches with 13 seconds left in the second round and advanced to the semifinals, where he faced the reigning Krush Bantamweight champion Koji Ikeda. Ishii won the fight by unanimous decision, with scores of 30–29, 30–29 and 30–28. He advanced to the finals, where he faced the 2021 K-1 Japan Grand Prix winner Toma Kuroda. He lost the fight by split decision, after an extra fourth round was contested.

Ishii faced Yodsila Chor.Hapayak at K-1 World GP 2023: K'Festa 6 on March 12, 2023. Originally a unanimous decision loss for Ishii, the bout was later changed to a technical draw due to the second round knockdown being against the rules as it followed an illegal kick catch. The bout was rejudged without taking consideration of the second round and was declared a majority draw.

Ishii was expected to face Puen Sakyothin at BOM 40 on May 14, 2023. Puen withdrew from the bout on May 5, due to visa issues, and was replaced by Wasinchai SomsakKorsang. He won the fight by a first-round knockout.

Ishii made his Rajadamnern World Series debut against Eaktawan Sitcharnsing on July 22, 2023. He won the fight by a first-round knockout. Ishii made his next Rajadamnern World Series appearance against JJ Or.Pimonsri on September 9, 2023. He won the fight by a second-round knockout.

Ishii faced Pangtor Por.Lakboon at an October 28, 2023, Rajadamnern World Series event. He lost the fight by unanimous decision.

Ishii challenged the K-1 Bantamweight champion Toma Kuroda at K-1 ReBIRTH 2 on December 9, 2023. He lost the fight by unanimous decision.

Ishii faced Nampetch Chor.Champion at TOP BRIGHTS 1 on January 21, 2024. He won the fight by a first-round knockout.

Ishii faced Ryuki Matsuda at a Rajadamnern World Series Japan on April 14, 2024. The fight was ruled a unanimous decision draw.

Ishii faced Yusei Shirahata at K-1 Dontaku on July 13, 2025. He won the fight by split decision, after an extra fourth round was fought.

Ishii faced the current Krush Bantamweight champion Eito Kurokawa for the vacant K-1 Bantamweight (-53kg) title at K-1 World MAX 2025 - 70kg World Championship Tournament Final on November 15, 2025. He won the fight by unanimous decision, with three scorecards of 28—26 in his favor.

Ishii made his first K-1 Bantamweight (-53kg) title defense against Zhang Jinhui at K-1 World GP 2026 -90kg World Tournament on February 8, 2026. He retained the title by unanimous decision, with three scores of 30—29 in his favor.

Championships and accomplishments Amateur 2010 WINDY Super Fight -30 kg Champion 2010 M-1 -35 kg Champion 2010 King of Strikers -35 kg Champion 2011 Windy Super Fight -35 kg Champion 2011 TRIBELATE -35 kg Champion 2011 M-1 Junior -35 kg Champion 2011 King of Strikers -40 kg Champion 2012 Windy Kick Jr 40 kg Champion 2013 GLADIATOR Kick Jr 45 kg 2013 Trang Province 45 kg Champion

Professional Punpanmuang 2014 Punpanmuang Mini Flyweight Champion True4U Muaymanwansuk 2017 True4U Flyweight Champion KNOCK OUT 2018 KING OF KNOCK OUT Flyweight Champion 2019 IBF Muay Thai World Flyweight Champion World Professional Muaythai Federation 2019 WPMF World Flyweight Champion 2020 WPMF World Super Flyweight Champion The Battle of Muay Thai 2020 Battle of Muay Thai Super Flyweight Champion (1 defense) World Boxing Council MuayThai 2022 WBC MuayThai World Super Flyweight Champion K-1 2022 K-1 Bantamweight World Grand Prix Runner-up 2025 K-1 Bantamweight Champion. One successful title defense

Fight record

Amateur record 2013-03-16 Win Kasem Kalamram 5th Muay Thai World Championship, Final Bangkok, Thailand Decision 3 1:30 2013-02-24 Win Kim Hyun Song GLADIATOR 51 Fukuoka, Japan TKO 1 1:30 2012-12-24 Win Japan Amateur Muaythai 2013 WMF World Championships Qualifying Competition Tokyo, Japan 2012-08-26 Loss Kaipet Suwan-Aharn-Peekmai JKMO - Japan Kick Muay Thai event Tokyo, Japan Extra Round Decision 2012-08-12 Loss Kaipet Suwan-Aharn-Peekmai Windy Kick Japan vs Thailand Saraburi Province, Thailand Decision 2012-07-22 Win Reiji Hazuma GLADIATOR 39 Fukuoka Prefecture, Japan Decision 3 3:00 2012-07-01 Win Takuma Ota Muay Thai WINDY Super Fight in NAGOYA～MuayThaiphoon!～ Nagoya, Japan KO (Front Kick) 1 2012-06-10 Win Kosuke Yamada Muay Thai WINDY Super Fight vol.12 Saraburi Province, Thailand Decision 5 1:30 2012-04-07 Loss Samingdam Sor.Kittibam Trang Province, Thailand Decision 5 2012-03-12 Win Muay Thai WINDY Super Fight Tokyo, Japan Decision 2012-02-26 Draw Chopperbank Rachanon Pattaya, Thailand Decision 5 2011-12-18 Loss Apichit Muay Thai WINDY Super Fight vol.10 2011 FINAL Tokyo, Japan Decision (Split) 5 1:30 2011-11-19 Win Chikara Iwao TRIBELATE vol.35 -Title Match Festival- Tokyo, Japan Ext.R Decision (Split) 3 2:00 2011-10-10 Win Hikaru Fujimoto KING OF STRIKERS Round 6 Fukuoka Prefecture, Japan Ext.R Decision 3 2:00 2011-09-23 Win Daigo Sunaga Muay Thai WINDY Super Fight vol.9 Nagoya, Japan Decision (Unanimous) 5 1:30 2011-07-31 Win Kunito Tsuchiya Muay Thai WINDY Super Fight vol.8 Tokyo, Japan Decision 2 2011-07-16 Win Chikara Iwao TRIBELATE vol.33 Tokyo, Japan Decision 32:00 2011-07-03 Win Kouki Yamada Muay Thai WINDY Super Fight in NAGOYA ～Muay Typhoon!～ Nagoya, Japan Decision (Unanimous) 2 2:00 2011-06-19 Win Shota Kuroki M-1 FAIRTEX SINGHA BEERMuay Thai Challenge Tokyo, Japan Decision 2 3:00 2011-04-10 Win Yuki Kono KING OF STRIKERS Round 4 Fukuoka Prefecture, Japan KO 3 2011-01-10 Win Rikuto Tsuyama M-1 Muay Thai Amateur Kyushu Fukuoka Prefecture, Japan KO 2 2010-11-07 Loss Chikara Iwao Muay Thai WINDY Super Fight vol.5 2010 FINAL Tokyo, Japan Decision (Majority) 2 2010-09-19 Loss Shota Kuroki Muay Thai WINDY Super Fight vol.4 Tokyo, Japan Decision 2010-06-14 Win Muay Thai WINDY Super Fight Vol.3 Tokyo, Japan Decision 2010-03-04 Loss Takahito Yamada Muay Thai WINDY Super Fight Vol.2 Tokyo, Japan Decision 2010-02-13 Win Denwanchai Wor.Wanchai Muay Thai WINDY Super Fight in Kyushu Kyushu, Japan KO (Right Cross) 3 Legend: