A strain of bacterium designated as Strain Dsp-2,capable of degrading chlorpyrifos efficiently,was isolated from sludge in a wastewater treatment installation that has long been treating chlorpyrifos polluted water.Strain Dsp-2 was identified preliminarily as Sphingomonas.sp based on its physiological and biochemical characters and the result of the 16 SrDNA homologue sequence analysis.Strain Dsp-2 can grow with chlorpyrifos as its sole carbon source,degrading 100 mg L^-1 of chlorpyrifos completely within 24 h.Results of its degradation characteristics show that the degradation rate of chlorpyrifos was increased considerably with the concentration.But when the chlprpyrifos concentration was higher than 200 mg L^-1,the strain Dsp-2 stopped degrading.Effects of initial inoculum size,yeast extract,glucose,peptone and metal ion on degradation of chlorpyrifos by Dsp-2 were also studied.Results show that large initial inoculum size and a proper amount of peptone could promote its degradation of chlorpyrifos.1 mmol L^-1 of Fe³⁺ and Ni²⁺ could restrain its degradation rate of chlorpyrifos.Addition of strain Dsp-2 to three test soils treated with chlorpyrifos resulted in a higher degradation rate of chlorpyrifos than in the control,soils without inoculation.However,the highest rate was showed in brown soil,which indicated moderate pH,moisture and nutrients could promote the degradation.The degradation rate reached to 85%～98% at 7th day when the concentration of chlorpyrifos ranged in 1～100 mg kg^-1.