The 2003 AIG Japan Open Tennis Championships was a combined men's and women's tennis tournament played on outdoor hard courts at the Ariake Coliseum in Tokyo in Japan that was part of the International Series Gold of the 2003 ATP Tour and of Tier III of the 2003 WTA Tour.

The tournament ran from September 29 through October 5, 2003.

Rainer Schüttler and Maria Sharapova won the singles title.

Rainer Schüttler defeated Sébastien Grosjean 7–6(7–5), 6–2 Maria Sharapova defeated Anikó Kapros 2–6, 6–2, 7–6(7–5) Justin Gimelstob / Nicolas Kiefer defeated Scott Humphries / Mark Merklein 6–7(6–8), 6–3, 7–6(7–4) Maria Sharapova / Tamarine Tanasugarn defeated Ansley Cargill / Ashley Harkleroad 7–6(7–1), 6–0