Abstract: After optimizing the reaction condition and parameters of RT-PCR,a cDNA clone of cytochrome P450s was obtained from total RNA of midgut of 6th instar larvae of fenvalerate resistant strain of Helicoverpa armigera,using specific primers from CYP6B7 gene. The cDNA has an open reading frame of 1515 nucleotides,encoding a protein of 504 amino acids residues (GenBank No. DQ497428).Comparing with previously reported CYP6B7 (GenBank No.AF031468),the similarity of nucleotides and identity of amino acids of sequence were 97.75% and 98.81%,respectively.The sequence was classified as an allele of CYP6B7.Northern Blotting analysis showed that the expression of CYP6B7 mRNA in HDFR strains of H.armigera was significantly higher than that of the HDS strain,suggesting that CYP6B7 played an important role in the resistance of H.armigera to fenvalerate.