He represented Japan at the 1996 Atlanta Olympics and managed to reach the semifinals of the 200 m and helped the 4×400 m relay to secure fifth place in the final in an Asian record time. He won his first major championship title in 1997, winning the 200 m gold at the East Asian Games, but he did not get past the heat stages at either the IAAF World Indoor Championships or the World Championships in Athletics.
Ito also clocked a personal best of 20.16 s in the 200 m on 2 October 1998 at Kumamoto, Japan. He put in a strong performance at the 1999 World Indoor Championships, just missing out on the 60 metres final and running an Asian indoor record time for fifth place in the 200 m competition. At the 2000 Sydney Olympics, Ito finished seventh in the semi-finals in both the 100 m and 200 m events (10.39 s and 20.67 s respectively) ; the Japanese men's 4 × 100 m team (Nobuharu Asahara, Koji Ito, Shigeyuki Kojima, Shingo Suetsugu) finished sixth in 38.66 s. Suetsugu later went on to follow in Ito's footsteps as Japan's top male sprinter. Ito never again matched the form of his high-water-mark 1998 season and retired in 2002.
