Jae Hee began his acting career as a child actor in the 1997 drama Mountain. He continued to appear on television, such as in the campus drama School 2 and the family sitcom Wuri’s Family, as well as the 2000 horror film Bloody Beach.

In 2004, Jae was cast as the lead actor in Kim Ki-duk’s 3-Iron, playing a silent young man who breaks into vacant houses and while living there for a few days, he cleans the house and repairs broken gadgets during his stay. The art house film won critical acclaim both locally and internationally. For his performance, Jae Hee was named Best New Actor at the Blue Dragon Film Awards.

But Jae Hee’s breakout role would come in 2005, when he played the playful but loyal Lee Mong-ryong in Sassy Girl Chun-hyang, a modernized romantic comedy based on the well-known folktale Chunhyangjeon.  It became a huge hit not only in Korea, but throughout Asia, making him and co-star Han Chae-young into Korean Wave stars.

Jae followed that with action comedy film The Art of Fighting in 2006, in which he played a bullied high school kid who learns about martial arts and life from a wizened mentor (played by veteran actor Baek Yoon-sik).

Jae Hee returned to television, playing a chef in 2007’s Witch Yoo Hee (in which he reunited with Chun-hyang director Jeon Ki-sang), and a surrogate father in 2008’s One Mom and Three Dads, but those series were less successful ratings-wise.

On August 5, 2008 Jae enlisted for mandatory military service. He was assigned to the Defense Media Agency until his discharge on June 18, 2010.