Seiji Inagaki (稲垣誠司, Inagaki Seiji, born 28 April 1973)is a retired Japanese athlete who specialized in the 400 metres hurdles.

He won bronze medals in 4 × 400 metres relay in two editions of the World Indoor Championships; in 1993 with teammates Masayoshi Kan, Yoshihiko Saito and Hiroyuki Hayashi and in 1995 with Kan, Hayashi and Tomonari Ono. He also competed in the same event at the 1997 World Championships without reaching the final.^[1]