Honma had his first mixed martial arts fight on May 12, 1990, competing for the Shooto organisation in Japan. Honma compiled a record 3-3-2 in Shooto, including a victory over Manabu Yamada. He lost to Rene Rooze in his K-1 debut in 1995. On October 11, 1998, Honma made his Pride FC debut at Pride 4. Honma beat Naoki Sano by TKO. On June 6, 1999, Honma beat Wayne Turner in a kickboxing match at K-1 Survival '99. Honma would go on to lose at Pride 5 to Francisco Bueno by TKO. On April 14, 2000, Honma lost to Ron Waterman by decision at UFC 25. His final career fight was on July 4, 2004 against Ken Orihashi; the fight ended in a draw.