However, he signed with the UFC in 1998, after his Pancrase career. Rutten was originally told about Ultimate Fighting Championship (UFC) before its first event in 1993, when would-be UFC competitor Ken Shamrock proposed it to him, but Rutten decided to stay in Pancrase, as he felt the 'no rules' format was too dangerous and he did not want to risk his career so early. Fuke took Rutten down and locked an armbar, which forced the Dutch fighter to spend a rope escape, though Bas was eventually able to land a knee strike to the liver to finish the match with a win. Rutten's second match, however, would be against a more experienced opponent, Takaku Fuke, and it would expose his main weakness, which was his lack of groundfighting experience. The KO was so brutal that Yanagisawa was carried from the ring and spent two days in hospital, with Bas himself fearing for his life.

In September 1993, Rutten had his debut in Pancrase against the 45lb heavier Ryushi Yanagisawa, knocking him out with palms and knee strikes in only 48 seconds. A precursor to modern mixed martial arts, the organization was the first of its kind and featured fighting with no closed fisted strikes to the face, and boasted early MMA names Frank Shamrock, Vernon White, Maurice Smith, Ken Shamrock, and Guy Mezger. In 1993, when Japanese pro wrestlers Masakatsu Funaki and Minoru Suzuki traveled to the Netherlands to scout fighters for their new 'hybrid wrestling' organization, Pancrase, Rutten was immediately chosen. Though his first training was a difficult start for him, he focused in learning the rudiments of the art. He was scouted by Chris Dolman and invited to train at the Fighting Network RINGS Holland dojo. Rutten began his professional mixed martial arts career when he was working as an entertainer.

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