光裂合酶（Photolyases，EC 4.1.99.3）为一种DNA修复酵素，专门修复遭受紫外线破坏的DNA。此酵素的作用需要可见光的协助，最好是在蓝紫光下，此现象称为光致活作用（photoreactivation）。

由系统发生学来看，光裂合酶为一个相当古老的酵素，从细菌、真菌，到动物体内都有，在植物体内尤为重要。但人和其他胎盘哺乳类体内却改以另一种较无效率的核苷酸切除修复法来取代光裂合酶，因此并无此酵素活性。

在DNA中，相邻的胸腺嘧啶受到紫外线的照射时，会形成共价键，形成环丁烷桥，称为胸腺嘧啶二聚体，导致基因病变。光裂合酶会接在DNA上，切除胸腺嘧啶二聚体。

Photolyases (EC 4.1.99.3) are DNA repair enzymes that repair damage caused by exposure to ultraviolet light. This enzyme mechanism requires visible light, preferentially from the violet/blue end of the spectrum, and is known as photoreactivation.

Photolyase is a phylogenetically old enzyme which is present and functional in many species, from the bacteria to the fungi to plants and to the animals. Photolyase is particularly important in repairing UV induced damage in plants. The photolyase mechanism is no longer working in humans and other placental mammals who instead rely on the less efficient nucleotide excision repair mechanism.