乐思晦（？ - 691年），唐朝雍州长安人，在武周武则天在位期间，691年担任宰相（同凤阁鸾台平章事）。

其父乐彦玮在唐高宗在位时曾担任宰相。691年，武则天任命乐思晦为鸾台侍郎（黄门侍郎）、同凤阁鸾台平章事。四个月后，乐思晦被处死，他不到十岁的儿子，被发往司农寺为奴。乐思晦之子在左台中丞来俊臣诬告同平章事任知古、狄仁杰、裴行本、司农卿崔宣礼、前文昌左丞卢献、御史中丞魏元忠、潞州刺史李嗣真七位大臣谋反的时候，上书武则天：「臣父已死，臣家已破，但惜陛下法为俊臣等所弄。陛下不信臣言，乞择朝臣之忠清、陛下素所信任者，为反状以付俊臣，无不承反矣。」武则天心有所动，最终决定召见七位大臣，询问为何狱中已自承谋反。

Le Sihui (乐思晦) (died 691) was an official during Wu Zetian's Zhou Dynasty, briefly serving as chancellor.

It is not known when Le Sihui was born. His father Le Yanwei served as chancellor during the reign of Wu Zetian's husband Emperor Gaozong of Tang. In 691, after Wu Zetian had herself assumed the title of "emperor" in 690, Le Sihui was Luantai Shilang (鸾台侍郎), the deputy head of the examination bureau of government (鸾台, Luantai), when Wu Zetian gave him the designation of Tong Fengge Luantai Pingzhangshi (同凤阁鸾台平章事), making him a chancellor de facto. About four months later, however, for reasons lost to history, he was executed. (His son, who was not yet 10 years old and whose name is lost to history, was made a servant at the ministry of agriculture, and in 692 was instrumental in submitting a petition to persuade Wu Zetian to release the officials Ren Zhigu, Di Renjie, Pei Xingben, Cui Xuanli (崔宣礼), Lu Xian (卢献), Wei Yuanzhong, and Li Sizhen (李嗣真) after they had been arrested on suspicion of treason.)