Hero's 5: 2006 Lightweight Grand Prix Opening Round was a mixed martial arts event held by the Hero's promotion on May 3, 2006 at the Yoyogi National Gymnasium in Tokyo, Japan. The opening round of the 2006 Lightweight Grand Prix was held at the event. Originally, Gilbert Melendez was scheduled to compete in the Grand Prix but was forced out with a leg injury and replaced by Rani Yahya. Also, Yoshihisa Yamamoto was set to face Wakashoyo at the event but was ordered by doctors not to compete due to a strained back. Kazuhiro Hamanaka took his place instead.