The present invention provides a method for preparing a hybrid gene. The method includes a step of amplifying a P450 gene fragment contained in a sample using primers designed on the basis of regions of a plurality of P450 in which amino acid sequences are highly conserved and a step of preparing the hybrid gene using the amplified fragments and a known P450 gene. The method includes no culturing step or a step of normalizing extracted DNAs and is useful in isolating a P450 gene from various microbial resources. The present invention further provides a fused cytochrome P450 monooxygenase containing a peptide which is linked to the C-terminus of a P450 protein with a linker portion disposed therebetween and which has the same function as that of a reductase domain contained in a cytochrome P450 monooxygenase originating from Rhodococcus sp. strain NCIMB 9784. This enables the construction of a high-efficiency electron transfer system useful for various P450 proteins and also enables the production of an active P450 monooxygenase.
