曲沃桓叔（前802年 - 前731年），姬姓，名成師，謚為「桓」，晉國晉穆侯之子，曲沃的君主。

前745年晉昭侯把曲沃（在今中國山西省曲沃縣）封給其叔成師，時年58歲，因「好德」而得民心。前739年晉大臣潘父弒殺了晉昭侯，迎立曲沃桓叔。桓叔欲入晉，晉人發兵攻桓叔，桓叔退回曲沃。晉人共立昭侯子公子平為君，是為孝侯。前731年曲沃桓叔去世。

桓叔之孫曲沃武公起兵滅晉，世稱晉武公，從此曲沃與晉國合併。桓叔庶子韓武子，乃戰國七雄的韓國的先祖。

Huan Shu of Quwo (曲沃桓叔 Qūwò Huán Shū, 802–731 BC), ancestral name Ji (姬), given name Chengshi (成師), was the first ruler of the state of Quwo during the Spring and Autumn period. He was the son of Marquis Mu of Jin and uncle of Marquis Zhao of Jin.

In 745 BC, the first year of the reign of Marquis Zhao of Jin, Marquis Zhao enfeoffed Chengshi at Quwo (around modern Quwo County, Shanxi). He was then known as Huan Shu of Quwo. He was then 58 years old. He was said to be a benevolent ruler beloved by the people of Quwo.

In 739 BC, the seventh year of his reign, a Jin official named Panfu (潘父) murdered Marquis Zhao and invited Huan Shu to ascend the throne of Jin. He accepted Panfu's welcome and attempted to enter Jin, but he was defeated by the Jin troops and retreated to Quwo. Then, the Jin people asked the son of Marquis Zhao of Jin, Ping, to ascend the throne and he became the next marquis: Marquis Xiao of Jin.

In 731 BC, Huan Shu died and his son, Shan, ascended the throne as the next ruler of Quwo: Zhuang Bo of Quwo. Another son of Huan Shu, Han Wan, became the progenitor of the State of Han.