细胞色素P450（英语：cytochrome P450）超家族（官方缩写为CYP）是一大类多种多样的酶。大多数细胞色素P450酶的功能是催化氧化有机化合物。细胞色素P450的底物包括有：如脂质与甾体激素的代谢中间产物，亦有药物与其他毒性化学物质等非生物物质。细胞色素P450类是涉及药物代谢与生物激活作用的主要酶类，约占到各种代谢反应总数的75%。

由细胞色素P450催化的最常见反应就是单加氧酶反应，例如将氧气中的一个氧原子插入到有机底物（以RH表示）中，而另一个氧原子被还原形成水：

RH + O₂ + 2H + 2e → ROH + H₂O

Cytochromes P450 (CYPs) belong to the superfamily of proteins containing a heme cofactor and, therefore, are hemoproteins. CYPs use a variety of small and large molecules as substrates in enzymatic reactions. They are, in general, the terminal oxidase enzymes in electron transfer chains, broadly categorized as P450-containing systems. The term P450 is derived from the spectrophotometric peak at the wavelength of the absorption maximum of the enzyme (450 nm) when it is in the reduced state and complexed with CO.