After honing his submission skills under Satoru Sayama, Sato made his professional debut in MMA on December 7, 1994, winning over Michael McAuliffe with a calf slicer, the first time the move had been used in mixed martial arts.
Sato's winning streak finally broke in 1998 when he lost a highly publicized match to Canadian Jiu-Jitsu Champion Joel Gerson by a surprising armbar in the first round of a non-title event in 1998.
After returning to Japan, Sato got also which is thought to be the fastest submission victory in MMA history when he submitted Charles Diaz in a mere five seconds with a flying armbar.
Going into the second round, Sato controlled the stand-up, opening a cut on the right side of his opponent's face and scoring a takedown, but he found himself having to defend from his guard while Uno capitalized to land ground and pound.
At the third round, Uno started controlling the wrestling game and solidifying his assault to Sato's guard, and ultimately, when a clearly tired Rumina attempted a takedown, Caol took his back and locked a rear naked choke for the tap out.
The second round saw Gomi landing damaging punches, as well as Sato utilizing an active guard to counterattack, and the striker eventually bypassing his defenses and controlling the pace.
On July 10, 2009, Sato competed in a grappling super fight at the UFC 100 Fan Expo Grappler's Quest against Ulysses Gomez, winning by submission with an inverted triangle choke/wrist lock combination.