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 standing over Sato on his back, then striking him with a knee and a punch while he was getting up, knocking him out.
UFC
After his second victory over Rumina Sato, Uno was recruited to fight for the UFC's Bantamweight title against Jens Pulver. 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 Championship was vacated. A tournament was put together pitting the top Lightweights in the UFC. 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. Uno used angles and effective wrestling techniques to frustrate Penn, who appeared tentative from the start, while Penn was dominant in spurts. The fight was called a draw and neither fighter won the championship belt.
Uno was spotted in attendance at UFC 94, fueling talk of a return to the UFC's Lightweight division. It was later confirmed that Uno had signed with the UFC and would face Spencer Fisher at UFC 99: The Comeback. In spite of finishing the bout pounding Fisher with punches from top crucifix position, Uno lost by a controversial unanimous decision. Then, on November 21, 2009, Uno fought UFC newcomer Fabrício Camões to a majority draw at UFC 106. On March 31, 2010, Uno fought Gleison Tibau at UFC Fight Night 21. He was overpowered by the much bigger Tibau, and suffered a loss via TKO. After the fight he was released from the promotion.
Uno then signed up with All Japan Pro Wrestling in June 2002, where he debuted as a partner for Kendo Kashin against Kaz Hayashi and Kashin's double Mr. Problem, albeit in another losing effort. In November, he became also part of the event Wrestle-1, co-promoted with K-1. Coming under a monkey mask and the name "The Apeman Nigo", Uno teamed up with Kashin to defeat La Parka and Super Parka. He returned to AJPW in May 2003 under his Apeman Nigo persona. He and Kaz Hayashi lost to Kashin and Low Ki, but at the next event he teamed up with Ki to beat Gran Naniwa and Ryuji Hijikata. At the next day, he competed under his true name with Keiji Mutoh, winning over 728% Machine and The Apeman 200%, and then recovered his Nigo mask to team with Mutoh and Taka Michinoku in a winning effort against The Great Sasuke, The Great Kosuke and The Apeman. Uno's last appearance for AJPW would be in July, allying with Kashin and Robbie Brookside to beat Hayashi, Jimmy Yang and Ebessan.
