构象异构（英语：Conformational isomerism，又译结构异构或构形异构，为同分异构的一种类型，指由于原子环绕于化学键四周，而导致结构式相同，却具有化学构象或构象异构体之差异的分子现象。

有三种效应，会使某些构象异构物较为稳定：

不同的构象异构物，会因为键结位置的旋转而互相变换，且不会破坏化学键。以丁烷为例，其纽曼式投影（右图）可显示出主干（C-C键）周围各键结上之分子（C及C）之间的夹角变化。旋转异构物指构象异构物的各形式，旋转能障（rotation barrier）则为相互变换所需的活化能。

In chemistry, conformational isomerism is a form of stereoisomerism in which the isomers can be interconverted exclusively by rotations about formally single bonds (refer to figure on single bond rotation). Such isomers are generally referred to as conformational isomers or conformers and, specifically, as rotamers. Rotations about single bonds are restricted by a rotational energy barrier which must be overcome to interconvert one conformer to another. Conformational isomerism arises when the rotation about a single bond is relatively unhindered. That is, the energy barrier must be small enough for the interconversion to occur.