Youichi Ui learned to ride motorcycles in the Japanese pocket-bike and minibike series. National 125 Champion in 1995, Ui joined the Grand Prix the same year, but his early attempts were impeded by inferior machinery. Recruited by Derbi in 1999, the Japanese rider finished runner up in 2000 and again in 2001, tying a record for the most wins without a World Championship. Ui made three MotoGP appearances in 2004 on the Harris WCM team, with a best finish of 15th.