In Chang's first world title try, he lost to Hilario Zapata of Panama by a decision in 15 rounds in 1982. However, in a rematch held at Seoul, he avenged that loss and became world champion by knocking out Zapata in three rounds.
Chang then went on to establish a world record for the most defenses as a world Jr. Flyweight champion, defending the title successfully 16 times between 1983 and 1989.
Chang had a record of 38 wins, 4 losses and 1 draw, with 17 wins by knockout.