Abstract: Effects of single and combined pollution of chlorpyrifos and acetochlor on soil enzyme activity and microbial biomass carbon were investigated in an indoor simulation experiment.Results show that response to the pollution varied with the enzymes.The catalase was inhibited,while the urease was enhanced in activity under the stress of either single or combined pollution of chlorpyrifos and acetochlor.Both acidic phosphomonoesterase and alkaline phosphomonoesterase were first stimulated and then inhibited in the same condition.However,application of acetochlor alone showed the most significant inhibitive effect on catalase and acidic phosphomonoesterase.Soil microbial biomass carbon was enhanced under the stress of simple pollution of chlorpyrifos or acetochlor in the initial stage,but it was inhibited after 14 days in the presence of combined pollution.