溶细胞素（Cytolysin），亦作溶胞素，是一类由微生物、植物或动物分泌的对特定细胞有毒性的物质。这类物质通常是通过让靶细胞因裂解而溶解而起效的。通常，溶细胞素会因对某一类细胞具有特异性而获得相应的名称。举个例子来说，一类能够导致红细胞裂解并释放出的其胞内血红蛋白的溶细胞素就被命名为溶血素（Hemolysin）。溶细胞素在免疫中扮演着重要角色，一部分毒液中也含有溶细胞素。

部分细菌（比如李斯特菌）可以分泌溶细胞素。这些细菌分泌的溶细胞素可以破坏巨噬细胞的吞噬体膜，并逃逸到上述细胞的细胞质中。

Cytolysin refers to the substance secreted by microorganisms, plants or animals that is specifically toxic to individual cells, in many cases causing their dissolution through lysis. Cytolysins that have a specific action for certain cells are named accordingly. For instance, the cytolysins responsible for the destruction of red blood cells, thereby liberating hemoglobins, are named hemolysins, and so on. Cytolysins may be involved in immunity as well as in venoms.