We discovered 528 putative cytochrome P450s (P450s) in Oryza sativa L. ssp. indica using Arabidopsis thaliana P450s as database. Those putative rice P450s are thought to belong to 40 families classified in Arabidopsis thaliana. We compared distributions of Arabidopsis thaliana and Oryza sativa P450s and found the two species have similar distribution patterns. However, family distributions of two species also have some differences. For example, in rice, the gene number in families of CYP71, CYP72, CYP76, CYP89, CYP94 and CYP709 is more than twice that in Arabidopsis thaliana; and there are 33 CYP705 members in Arabidopsis thaliana but none in rice. We also found gene members in CYP71 and CYP81 are organized as tandem arrays repeated in the rice genome; maybe they are duplications in the evolutionary event. Furthermore, we accumulated expression sequence tag (EST) evidence for 263 putative rice P450s, which are expressed at transcriptional level and more likely to be true P450s.