The eldest of three Aoki brothers, Nobuatsu was introduced to motorcycle racing by his father. Aoki began his Grand Prix career in 1990 and took his first and only Grand Prix win at the 250cc Malaysian Grand Prix in 1993. His best season was his debut year in the 500cc category - 1997 with Rheos Elf-Honda, where he finished third behind Mick Doohan and Tadayuki Okada. He moved to Suzuki in 1998, and after 3 seasons, spent a year developing Bridgestone tyres until 2002 he when he joined the Proton-Team KR MotoGP team. Aoki remained with the Proton team for three seasons until leaving MotoGP full time, making appearances on the Suzuki team in 2005, 2007 and 2008.