Kaoru "Caol" Uno (born May 8, 1975) is a Japanese mixed martial artist. He was born in Kanagawa, Japan.Uno rose through the ranks of the Shooto mixed martial arts organization in Japan. In May 1999, Uno fought the then-legendary Rumina Sato. The fight was hailed as "Fight of the Year", an extremely fast-paced back and forth battle with a wide variety of stand-up and grappling exchanges. Eventually, Uno took the back of Sato and choked him into submission.

The two rematched in December 2000. This fight concluded with Uno throwing Sato on his back then striking him with a combination of kicks and punches, eventually knocking him out.

After his second victory over Rumina Sato, Uno was recruited to fight for the UFC's bantamweight (later renamed lightweight) title against Jens Pulver. Just days before the fight, a good friend of Pulver's, Dusty, died of cancer. Pulver promised Dusty that he would win the title for him.

In the fight, Pulver demonstrated what Olympic gold medalist Jeff Blatnick called "a different kind of strength" as he fought off Uno's trademark rear naked choke. Throughout the fight, Pulver stopped Uno's takedown attempts and pressed the action on the feet. Uno, who had earned a reputation as being "unflappable", began to show frustration for the first time in his career as Pulver neutralized all his offensive efforts. Pulver took a majority decision win in the fight.

After Pulver left the UFC, the lightweight title was vacated. A tournament was put together pitting the top-four 155 pounders in the UFC (B.J. Penn, Din Thomas, Matt Serra, and Caol Uno). In the first round, Uno faced Thomas. Thomas dominated the first round, setting a high pace. However, Uno turned things around, taking the second and third rounds to win the fight.

In the finals of the tournament, Uno faced Penn (who had previously defeated Uno by knockout in under 12 seconds). Uno used angles, and effective wrestling techniques to frustrate Penn, who appeared tentative from the start. Penn was dominant in spurts, and the fight was called a draw. This judges' decision was a disaster for the UFC management. As a result the division was temporarily abolished.