Isao Kobayashi is a Japanese mixed martial artist competing in the lightweight division.

Kobayashi won the 2009 Pancrase Neo-Blood Lightweight Tournament by first defeating Koji Nakamura at Pancrase - Changing Tour 3 and then Hirotaka Tomiyama at Pancrase - Changing Tour 4. Kobayashi later competed in and won the Pancrase 2011 Lightweight Grand Prix. Kobayashi first defeated Yukinari Tamura via split decision at Pancrase - Impressive Tour 4. He then faced Tomoyoshi Iwamiya at Pancrase - Impressive Tour 8 and won via unanimous decision. In the finals he faced Kazuki Tokudome, whom de defeated via TKO in the first round. In his next fight Kobayashi faced then-Pancrase Lightweight Championship Koji Oishi in a rematch. Kobayashi avenged his loss to Oishi and won the title by defeating Oshi via unanimous decision.

In March 2014 Kobayashi scored the biggest win of his career stopping the Shooto Welterweight (70 kg) Champion Kuniyoshi Hironaka with strikes in the main event of Pancrase 257, an event historical also because of it being the last Pancrase event being held in a ring.

On October 4, 2014, Kobayashi fought against Takeshi "Lion" Inoue Vale Tudo Japan: VTJ 6th. He won the fight via unanimous decision. Almost three months later Kobayashi would face Kazunori Yokota at DEEP - Dream Impact 2014: Omisoka Special on December 31, 2014. Kobayashi would lose via unanimous decision, his first loss in almost five years. 

Following the loss to Yokota, Kobabyashi would get back in the win column when he beat respected vet Marlon Sandro via split decision at Pancrase 266 on April 26, 2015.