Cholinesterase was screened from different animal tissues,and the characteristics of cholinesterase and the detecting conditions of organophosphorus pesticides were studied in this paper.The results showed that cholinesterase activity from donkey serum was high.Cholinesterase from donkey serum was chosen for the detection of organophosphorus pesticides.It is observed that the optimum temperature of enzymatic reaction was 35 ℃,and the optimum pH value range from7.5 to 8.0.The enzyme activity was not inhibited by excess butyryl thiocholineiodide,and the optimal concentration of substrate was 5 mmol/L.The enzyme activity was unchanged at 35℃ for 60 min,which showed the good thermal stability of the enzyme.IC50 of dichlorvos was 0.124 mg/mL and its inhibition time was 15 min.