酰肼（Hydrazide）是一类通式为(R₁=O)R₂-N-N-R₃R₄的有机含氮化合物，是肼类的酰基取代物。它们可以通过肼及衍生物与酰氯或酯反应制备：

酰肼与亚硝酸或亚硝酸酯加热时反应，生成酰基叠氮，发生Curtius重排反应转化为异氰酸酯，水解得到少一个碳的胺：

常见的酰肼有：对甲苯磺酰肼（1）、1,3,5-三异丙基苯磺酰肼（2）、异烟肼（3）、N,N'-二乙酰肼（4）、苯磺酰肼（5）、乙酰肼（6），见下图。醛酮转化为烯烃的Shapiro反应中也使用到了对甲苯磺酰肼。

Hydrazides in organic chemistry are a class of organic compounds sharing a common functional group characterized by a nitrogen to nitrogen covalent bond with 4 substituents with at least one of them being an acyl group. The general structure for a hydrazide is E(=O)-NR-NR₂, where the R's are frequently hydrogens. Hydrazides can be further classified by atom attached to the oxygen: carbohydrazides (R-C(=O)-NH-NH₂), sulfonohydrazides (R-S(=O)₂-NH-NH₂), and phosphonic dihydrazides (R-P(=O)(-NH-NH₂)₂. The related hydrazines do not carry an acyl group. Some important members of this class are sulfonylhydrazides such as p-toluenesulfonylhydrazide which are useful reagents in organic chemistry such as in the Shapiro reaction. This reagent can be prepared by reaction of tosyl chloride with hydrazine.