A bacterial strain Bacillus latersprorus DSP capable of degrading chlorpyrifos was isolated from soil.Degradation characteristics of chlorpyrifos by the strain DSP were investigated in pure culture system under conditions of pH 7.0,25℃ and biomass of OD₄₁₅ 0.2.The half-life of chlorpyrifos at concentrations of 1 and 10 mg L-1 was measured to be 1.48 d and 5.00 d, respectively.The chemical showed obvious inhibitive effect on degradation capability of the strain,when its concentration reached as high as 100 mg L^-1.The degradation rate of chlorpyrifos by the Strain DSP was affected by pH and temperature showing an order of pH 7.0>pH 5.0>pH 9.0,and of 35℃>25℃>15℃,respectively.A plasmid with a size of approximately 20 kb was found in Strain DSP.The strain lost its ability to degrade chlorpyrifos when the plasmid was removed by acridine orange and heating.When the plasmid was transferred into Escherichia coli JM109 and back into plasmid-removed DSP the transformants obtained the ability to degrade chlorpyrifos.These observations indicated that the plasmid of Strain DSP is responsible for the degradation of chlorpyrifos.