Our previous studies have found that the levels of cytochrome P450 and oxidative activities of cytochrome P450 monooxygenases were enhanced in a fenvalerate-resistant strain (HDFR) of Helicoverpa armigera (Hubner) in China, comparing with those of a susceptible strain (HDS). Here, we report the molecular cloning and gene expression of a specific P450 CYP6B7 from HDFR and HDS strain of H. armigera. Comparison of the deduced amino acid sequence showed that there were three substitutions of amino acids in the coding region of CYP6B7 cDNA of HDFR strain, comparing with that of HDS strain. Meanwhile, there were three mutative nucleotides in the intron of CYP6B7 genomic DNA in HDFR strain. Northern blotting analysis showed that the expression of CYP6B7 mRNA in HDFR strain of H. armigera was more than 5-fold higher than that in HDS strain. Further studies indicated that the expression of CYP6B7 mRNA increased as the larvae developed; however, it was rarely detected in the pupae and adult stages. The results suggested that cytochrome P450 CYP6B7 plays an important role in the pyrethroid insecticide fenvalerate resistance of HDFR strain of H. armigera; over-expression of CYP6B7 combined with relevant substitution of amino acids might be responsible for fenvalerate-resistance in H. armigera from China.