乐果（英文：Dimethoate）是一种常见的有机磷农药，化学名为：O,O-二甲基-S-（N-甲基氨基甲酰甲基）二硫代磷酸酯。很臭，杀虫作用好，特别是杀蚜虫、螟虫和螨效果特别好，而且对人的毒性比较低。具有抗胆碱酯酶功能。

Dimethoate is a widely used organophosphate insecticide and acaricide. It was patented and introduced in the 1950s by American Cyanamid. Like other organophosphates, dimethoate is an acetylcholinesterase inhibitor which disables cholinesterase, an enzyme essential for central nervous system function. It acts both by contact and through ingestion. It is readily absorbed and distributed throughout plant tissues, but is degraded relatively rapidly.