Plant cytochrome P450 monooxygenases constitute one of the largest families of protein genes involved in plant growth， development and acclimation to biotic and abiotic stresses. However， whether these genes respond to organic toxic compounds and their biological functions for detoxifying toxic compounds such as herbicides in rice are poorly understood. The present study identified 201 genes encoding cytochrome P450s from an atrazine-exposed rice transcriptome through high-throughput sequencing. Of these， 69 cytochrome P450 genes were validated by microarray and some of them were confirmed by real time PCR. Activities of NADPH-cytochrome P450 reductase (CPR) and p-nitroanisole O-demethylase (PNOD) related to toxicity were determined and significantly induced by atrazine exposure. To dissect the mechanism underlying atrazine modification and detoxification by P450， metabolites (or derivatives) of atrazine in plants were analyzed by ultra performance liquid chromatography mass spectrometry (UPLC/MS). Major metabolites comprised desmethylatrazine (DMA)， desethylatrazine (DEA)， desisopropylatrazine (DIA)， hydroxyatrazine (HA)， hydroxyethylatrazine (HEA) and hydroxyisopropylatrazine (HIA). All of them were chemically modified by P450s. Furthermore， two specific inhibitors of piperonyl butoxide (PBO) and malathion (MAL) were used to assess the correlation between the P450s activity and rice responses including accumulation of atrazine in tissues， shoot and root growth and detoxification.