In 1985, Oh won the light flyweight gold medal at the Boxing World Cup.

He defeated 1983 Pan American Games gold medalist Rafael Ramos in the semifinal bout.

In the preliminary bout, he beat Róbert Isaszegi, who won bronze at the 1988 Olympics, by RSC, scoring three knockdowns in the first round.

He lost in the semi-final to Luis Román Rolón who was later disqualified after failing a drug test.

[1][2] Oh competed at the 1988 Summer Olympics where he was a favorite to medal, however, he was eliminated in his first bout by a narrow 3–2 decision against eventual silver medalist and future hall of fame champion Michael Carbajal.