Lee was born in the Bundang district of Seongnam, Gyeonggi-do, South Korea. In the summer of 2001, 13 year old Lee successfully signed a contract with SM Entertainment after she won the category of "Best Feature" in the SM Entertainment Best Youth contest. For the contest, she acted out a monologue, singing to Dana The Grace's "Until the End of the World", and also did freestyle modeling poses. After she joined the company, she began intense training lessons on acting, singing, and dancing.
Lee's big break came in the form of the movie 'A Millionaire's First Love' playing the lead opposite popular actor Hyun Bin. Through it, she also made her singing debut, singing "Do Re Mi" from The Sound of Music in the movie and "Insa" on the original sound track.
In 2007, soon after the debut of labelmates Girls' Generation, she revealed that if she had not decided to continue her career as an actress, she would've become a member of Girls' Generation, as they have trained together when they were still trainees.