In the 2004/05 season Lee made his debut in the World Cup. Over the 1000 meters she was able to achieve respectable successes such as an 11th place in December 2004 at the World Cup in Harbin . She is far more successful over the 500 meters. Here she was able to achieve several places on the podium in the World Cup. She even won her first World Cup over 100 meters at the World Cup finals in March 2006. In the overall World Cup she also achieved an outstanding result with second place, which was supplemented with sixth overall place over the 500 meters. At the national South Korean championships in 2004 and 2005 she was five times national champion and once runner-up. In 2005 she set a junior world record over 100 meters, over 500 m she even improved her own world record within two days.
At the 2006 Winter Olympics in Turin , Lee took fifth place over 2 × 500 meters, at the individual distance world championships in 2007 and 2008 she just missed the bronze medal and took fourth place over 2 × 500 meters.