In 2008, Kim was cast in his first lead-acting role in the Korean drama Boys Over Flowers. 2008–2010: Career breakthrough and success
They left the show at the end of 2008 to focus on other projects.
Dubbed the "Lettuce Couple," the pair was popular among viewers and won the Best Couple Award at the 2008 MBC Entertainment Awards. In 2008, Kim joined the cast of the reality variety show We Got Married, where he was paired with singer Hwangbo. In January 2008, the group received a Newcomer Award at the Japan Gold Disc Award ceremony, making them one of only a few South Korean artists to win this award. The following year, in 2007, SS501 debuted in Japan with the single " Kokoro," which reached number five on the Oricon charts. The group quickly gained popularity, winning multiple new artist awards in 20. Their second EP, Snow Prince was released in late 2005, five months after their debut. Kim made his debut as a member of SS501 on June 23, 2005, with the group's first EP, Warning, released by DSP Media. After dropping out of university to focus on work, Kim enrolled in Chungwoon University in 2011 to study stage production management. He later passed his high school exams and enrolled in Kyonggi University. He described himself as a studious child, but he dropped out of high school to pursue a career in music.