Oh had been acting in some university plays since 1989, while he was studying at Konkuk University. He joined Yeonwoo Stage in 1991, then subsequently appeared to Ride Together (동승), which was adapted from a drama of Ham Se-dŏk. After his admission to K-ARTS in 1994, he continued his acting in Marionette Show (꼭두각시 놀음), The Story of Park Ki-hong (박기홍 이야기), Mud (진흙) and so on. During this period, he worked with Song Kang-ho; a source reported that both used to share a house. Other than plays, Oh played supporting roles in independent films, including Yellow Flower (둘 하나 섹스) and A Woman Off Her Uniform (남산에 오르다).
