The methanol extract from the Aconitum kusnezoffii Rchb. was isolated with system solvent method and the stomach toxicity of the four extracts on Lymantria dispar was determined with feed toxicity method. Then the effects of ethyl acetate extract from A. kusnezoffii on activities of the detoxification enzyme,protective enzyme and digestive enzyme in Lymantria dispar larvae were studied. The results showed that ethyl acetate extract from A. kusnezoffii had obvious insecticidal activity against gypsy moth and was the main insecticidal active substance. After treated with ethyl acetate extract from A. kusnezoffii at a dose of sub-concentration (LC20),the activities of carboxylesterase,glutathione S-transferases and acetylcholinesterase in the body showed continuous inhibition. The inhibition rate of acetylcholinesterase after 72 h treatment was 50.6% of the control,which was extremely significant (P＜0.01). The activities of superoxide dismutase,catalase,and peroxidase were first activated and then inhibited. The activation rate of catalase was extremely significant (P＜0.01) at 24 h treatment,which was 1.613 times of the control. The inhibition rate of superoxide dismutase at 72 h treatment was 84.2% of the control,which was also extremely significant (P＜0.01). The activities of lipase and amylase were consistently inhibited,with the inhibition rate of lipase at 72 h of 53.9% of the control,which was extremely significant (P＜0.01). The protease activity was inhibited after activation,with the activation at 24 h treatment of 1.431 times of the control,which was extremely significant (P＜0.01). The protease activity was inhibited at 72 h with 90.4% of the control,which was significant (P＜0.05). It is indicated that ethyl acetate extract from A. kusnezoffii affects detoxification enzymes,protective enzymes and digestive enzymes of gypsy moth larvae,and disturbs its normal physiological metabolism.