A strain DSP3 capable of utilizing chlorpyrifos as the sole carbon and energy sources was isolated. Based on the results of phenotypic features, phylogenetic of 16S rDNA sequence, DNA (G + C) mol% and DNA homology between strain DSP3 and reference strains, the strain DSP3 is identified as Alcaligenes faecalis. The degradation rate of chlorpyrifos was at 98.6% (100 mg/L) in liquid culture medium within 18 days and nearly 100% (100 mg/kg) in soil within 20 days respectively. An addition of strain DSP3 (10(8) cells/g) to soil resulted in a higher degradation rate than noninoculated soils. The different degrading rate of chlorpyrifos in four types of treated soils suggests that the dissipation is mediated by the activity of the soil microorganisms.