细胞色素c（英语：cytochrome c, cyt c）或称细胞色素复合体（英语：cytochrome complex），是一种血红素蛋白，属于cytochrome c family。细胞色素c会与粒线体内膜轻微连接，结构松散而微小的它和其他细胞色素不同，是一种高度可溶性蛋白，在水中的可溶性达每公升100克。细胞色素c是电子传递链不可或缺的组件，负责携带一粒电子，在复合物III和复合物IV之间传递。此外，它能够接受氧化和还原反应，但不与氧结合。在人体中，细胞色素c已经由CYCS基因完成编码。

细胞色素c和细胞进程性死亡有关。

The cytochrome complex, or cyt c is a small hemeprotein found loosely associated with the inner membrane of the mitochondrion. It belongs to the cytochrome c family of proteins. Cytochrome c is highly water-soluble, unlike other cytochromes, and is an essential component of the electron transport chain, where it carries one electron. It is capable of undergoing oxidation and reduction, but does not bind oxygen. It transfers electrons between Complexes III (Coenzyme Q – Cyt C reductase) and IV (Cyt C oxidase). In humans, cytochrome c is encoded by the CYCS gene.