Abstract: The toxicity of Cinnamomum zexlanicum Nees acetone extract to Tetranychus piercei McGregor and its effects on several esterase were studied.The results show that the Cinnamomum zexlanicum acetone extract has a good activity to Tetranychus piercei.The LC₅₀ value is 3.5642mg／mL after 24 h of treatment；the corrected mortalities are respectively95.45% and 98.84%，85.23% and 90.70%，81.82% and 87.21% after 48 h and 72 h of treatment at 6.67mg／mL，4.44mg／mL and 3.34mg／mL concentrations；the results also indicate that Cinnamomum zexlanicum acetone extract significantly inhibits esterase，carboxylesterase，alkaline phosphate esterase and acid phosphate esterase activities in Tetranychus piercei under various acetone extract concentrations of 5.0μg／mL，4.0μg／mL，3.0μg／mL，2.0μg／mL and 1.0μg／mL；the higher the treatment concentration，the heavier the inhibition.