Yu Oh-seong (유오성) (b.September 11, 1968 in Gangwon), also spelled "Yu Oh-Sung", "Yoo Oh-Sung" is a South Korean actor.
Throughout the mid-1990s, Yoo Oh-sung complemented a career in television with minor roles in film. With his success playing a young gangster in the hit movie Beat (1997), Yoo's face became familiar to a new generation of moviegoers. The year 1999 was somewhat of a breakthrough for Yoo, as he took the lead role in the acclaimed comedy Gancheob Li Cheol-jin (1999) (The Spy) and also starred in the hugely successful Juyuso seubgyuksageun (1999) (Attack the Gas Station!). Yoo's latest role is his biggest, however, as the co-star in Kyung-Taek Kwak's smash hit Chingoo (2001) (Friend). His performance drew much attention and praise, and the film became the most successful Korean film in history. Yoo has also reportedly agreed to star in director Kwak's next feature, about a boxer from a poor background.