Ulsan O clan (Korean: 울산 오씨; Hanja: 蔚山 吳氏) was one of the Korean clans. Their Bon-gwan was in Ulsan. According to the research in 1985, the number of Ulsan O clan was 2696. Their founder was . was a 7th descendant of who was a founder of Haeju Oh clan. came over from China during Seongjong of Goryeo’s reign in Goryeo. passed Imperial examination during Chungnyeol of Goryeo’s reign in Goryeo. As a result, served as a munha sirang pyeongjangsa (Korean: 문하시랑평장사; Hanja: 門下侍郞平章事) and began Ulsan O clan. Then, was appointed as Prince of Hakseong (Hanja: 鶴城君) because he defeated Wokou.