酰基（英语：acyl group）是指从含氧酸，包括无机酸中除去一个或多个羟基基团的衍生的官能团。它包含一个强制性羰基和烷基。在有机化学中，酰基（IUPAC名：链烷酰基）通常是衍生自羧酸。因此，它具有结构式RCO-，其中R代表被附着到CO基用单键的烷基。虽然称呼几乎总是应用于有机化合物，但酰基原则上可以是来自于其它类型的酸如磺酸，膦酸。在最常见的安排，酰基连接到一个更大的分子片段，在这种情况下，碳和氧原子通过双键相连。

酰基指的是有机或无机含氧酸去掉羟基后剩下的一价原子团，通式为R-M(O)-。酰基与卤素原子、烷氧基、氨基或取代氨基及酰氧基结合可以分别获得酰卤、酯、酰胺和酸酐。

An acyl group (/ˈæsɪl/ or /ˈeɪsaɪl/) is a functional group derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids. It contains a double bonded oxygen atom and an alkyl group.

In organic chemistry, the acyl group (IUPAC name: alkanoyl) is usually derived from a carboxylic acid. Therefore, it has the formula RCO–, where R represents an alkyl group that is linked to the carbon atom of the group by a single bond. Although the term is almost always applied to organic compounds, acyl groups can in principle be derived from other types of acids such as sulfonic acids, phosphonic acids. In the most common arrangement, acyl groups are attached to a larger molecular fragment, in which case the carbon and oxygen atoms are linked by a double bond.