She took up golf at the age of fourteen, which is unusually late for a future professional golfer, but just a few years later, in 2000, she became the Korean Amateur Champion.

She won three events on the LPGA of Korea Tour in her rookie season of 2002 and topped the money list.

In 2004, Lee played on the second-tier Futures Tour in the United States, finishing 23rd on the money list, but she was able to win an LPGA Tour card for 2005 by finishing tied for 25th at the LPGA Final Qualifying Tournament.

She made a steady start to her rookie season and in July 2005 was a surprise finalist in the inaugural HSBC Women's World Match Play Championship, which she lost to Colombia's Marisa Baena by one hole.

Two weeks later she won for the first time on the LPGA Tour at the BMO Financial Group Canadian Women's Open.