Yu Sang (; 1643–1723[1]), alternatively Ryu Sang, courtesy name Yeojin (汝珍, 여진),[2] was a royal court physician and politician of the Korean Joseon dynasty. He was a smallpox specialist who successfully treated three Joseon kings.
In 1693, due to having cured Sukjong's smallpox, he was granted a political office. Later he became the governor of Seosan, Goyang, Hapcheon and Saknyeong.[2]
His experiences with smallpox are detailed in his book, Gogeum Gyeongheom Hwalyubang (古今經驗活幼方).[3]
Supernatural anecdotes featuring him and a divine being circulated due to his fame.[4]
He was a 23rd-generation descendant of the Munhwa Ryu clan.[3] His father Yu Gyeongjib (柳景緝) served as an observation officer (觀察使, gwanchalsa).[2] His son Yu Jungrim (柳重臨) was also a medical practitioner who also wrote the agricultural text Jeungbo sallim gyeongje.[5]