24 new cDNA sequences encoding cytochrome P450 were amplified respectively from deltamethrin-susceptible and -resistant strains of the mosquito, Culex pipiens pallens, with a pair of degenerate primers according to the conservative amino acid sequences of CYP4 in insects by RT-PCR. Studies of molecular systematics show that the 24 new genes (alleles) belong to CYP4C,CYP4D,CYP4H and CYP4J subfamilies of the CYP4 family, and they were named by Cytochrome P450 Nomenclature Committee. Among the new genes(alleles),CYP4C23 may be a pseudogene, CYP4H13 has a retained intron 58 nucleotides in length, and CYP4J4V1 has a stop coden(TAG) in frame near the 3′-end.