The 2003 Formula Nippon Championship was the thirty-first season of premier Japanese single-seater racing, and the eighth under the Formula Nippon moniker. The series was contested over 10 races at five venues, including the final races at Fuji Speedway before a comprehensive renovation of the circuit began later that year.
10 different teams and 21 different drivers competed in the series. For the first time, the series adopted a spec chassis supplied by Lola, who replaced Reynard as the series' chassis supplier.
Satoshi Motoyama of Team Impul won his third series championship, becoming only the third driver after Kazuyoshi Hoshino and Satoru Nakajima to win three or more championships in Japanese top formula racing. Motoyama also became the second driver to win both the Formula Nippon and All-Japan Grand Touring Car GT500 Championships in the same year.
All teams used tyres supplied by Bridgestone, Lola B03/51 chassis, and Mugen MF308 engines.
All races were held in Japan.