A cytochrome P450 was purified from microsomes of Rhodotorula minuta. The optical spectrum of the purified cytochrome was characteristic of a low-spin ferric heme protein. Isovalerate caused a type I spectral change in it. The amino-terminal sequence of the cytochrome was different from those of other known microsomal cytochrome P450s. These results indicate that the cytochrome, which is tentatively named P450rm, is a novel species of cytochrome P450.