As a junior at Dongsan High School in Incheon, South Korea, Lee was selected by the Hyundai Unicorns with the 26th pick in the 2nd round (34th overall) of the 2002 KBO Draft.

As a freshman at Inha University in 2002, Lee made his first appearance for the South Korea national baseball team at the 2002 Intercontinental Cup.

Lee, the youngest player on the roster, helped his team to claim the silver medal, coming on in relief as a left-handed specialist and pitching four scoreless innings in the tourney.

Lee was signed by the Hyundai Unicorns in 2006 and had a successful rookie season as a setup man and left-handed specialist, appearing in 70 games and being 3rd in the KBO league in holds with 19.

In 2011 Lee spent the entire season in relief, compiling a 3–5 record with four saves, six holds and a 4.82 ERA in 74.2 innings of work spread over 50 appearances.