Lee Ok-Sung (born February 7, 1981 in Jinju, Gyeongsangnam-do, South Korea ) is a South Korean amateur boxer best known for winning the 2005 World Championships at flyweight.
At the 2006 Asian Games Lee just as surprisingly lost to Yang Bo of China in the quarterfinals, and his winning streak in international competition ended at 28 games.
He didn't participated in the national trials for the 2007 World Championships in order to complete his Master's degree.
In the first round of the 2008 Olympic Games Lee defeated 2007 World Champion Rau'shee Warren in another surprising upset victory.