Acetylcholinesterase (AChE) is the target site for the organophosphates and carbamates in insects. Widespread use of these two classes of insecticides has led to the selection of resistance. Target modification was regarded as a molecular mechanism in some resistance species. The altered AChEs with reduced sensitivity to inhibition are related to this resistance. AChE genes from two insecticide-resistant housefly (Musca domestica) strains D3 and Kash were isolated and sequenced using RT-PCR and streptavidin-linked magnetic bead techniques. The cDNAs have a 2082-bp open reading frame from which the complete amino acid sequence of AChE has been deduced. Some differences in nucleotide sequence and four-point mutations of amino acid were found compared to a susceptible strain, i.e., the Cooper strain. Three substitutions are likely to confer insecticide insensitivity, which seems that D3 and Kash belong to CH2 pattern of resistance.