Acting Career Siwon

After Siwon's appearances in Eighteen, Twenty-Nine and Precious Family, he was casted in a larger role for the mini-series Spring Waltz, playing the supporting role Park Sang-woo, the teenage cousin of a diligent and working young woman. Not long after Siwon's musical debut, he was casted in a large supporting role in the Hong Kong epic film A Battle of Wits as Prince Liang Shi, starring opposite Andy Lau. The cast promoted the movie throughout China with a short tour of four cities in November 2006. While the film received mixed reviews, Siwon garnered positive notices for his performance. He also received praises from co-star Lau, stating that Siwon is a wonderful actor and that he sets a good example for young Hong Kong idols.

Half a year after the release of A Battle of Wits, Siwon starred in the high school mystery/comedy film Attack on the Pin-Up Boys with other Super Junior members. He played one of the lead roles as a controlling and severe class president who was one of the popular possible subjects of being attacked by mysterious forces. Despite positive critical ratings, that film did not do well in the box-office, but all four versions of the film's DVD were all sold out and broke chart records.A few months later, Siwon was cast in mini-drama Legend of Hyang Dan as the lead role, Lee Mong-ryong.

In January 2010, Siwon starred in the SBS drama Oh My Lady!. It is a romantic comedy about a top star who finds himself living with his manager, a 35 year old woman who is trying to earn money to get custody of her child. He also starred as Agent Kim Jun-Ho, a data analyst and rookie elite agent in the drama Athena, a spin-off of drama Iris. Both roles portrayed by him earned highly positive praises from critics, senior actors, and fans alike. There is speculation in whether the series will be reintroduced in a second season, with Siwon playing a much larger role.

His acting career also extends into various music videos for fellow label mates, such as Girls' Generation's "Hoot", and Zhang Liyin and TVXQ's Xiah's duet "Timeless", where Siwon starred along with fellow Super Junior member Han Geng, which received critical praise. Siwon also made appearances in several commercial films, as well as guest appearing or hosting TV shows.

In April 2011, Siwon began filming for the Taiwanese drama Skip Beat! (Chinese: 華麗的挑戰) with Ivy Chen and fellow band member Donghae as the three main characters. It is a live-action adaptation of Japanese shōjo manga Skip Beat! by Yoshiki Nakamura and filming took place in Taiwan.

On August 1, Siwon has been confirmed to be the male lead character in a new KBS drama Poseidon alongside Lee Siyoung and Lee Sungjae. In the drama, he is a part of the #9 Investigation Team, a maritime police unit. Much media attention was placed on Poseidon as it was South Korea's first drama regarding the maritime police. Siwon received praises from his fellow cast members as well as the production team for his commendable acting and friendly conduct on set. Poseidon was broadcast on 19 October 2011 to 8 November 2011. Due to busy filming schedules that collide with Super Junior's activities, it was decided that Siwon will cease the latter during the duration of filming.