Abstract: To investigate the effects of sublethal concentration of beta-cypermethrin on activities of detoxifying enzymes in Carposina sasakii Matsumura adults, the C. sasakii adults were treated with LC10, LC20 or LC40 concentrations of beta-cypermethrin using residual film method. The activities of three detoxifying enzymes were then determined. 24 h after the treatments, the adults were transferred to clean conditions. The activities of the carboxylesterase (CarE), glutathione S-transferases (GSTs) and ethoxycoumarin O-de-ethylase (ECOD) in the adults mentioned above were investigated after 0, 6, 12 and 24 h, respectively. The results showed that activities of ECOD were inhibited significantly 24 h after the treatments. As the beta-cypermethrin concentration increases, the activities of ECOD were induced gradually especially for the LC40-beta-cypermethrin treated adults whose ECOD activity was significantly higher than that of the beta-cypermethrin-free controls. Additionally, the activities of CarE and GSTs in male moths increased. The activities were inhibited in females after treated with LC20 or LC40 concentration of beta-cypermethrin. After beta-cypermethrin treatment, the activities of the detoxifying enzymes were increased at the beginning and then decreased. Moreover, the activities of three detoxifying enzymes in adults fluctuated more significantly with the increase of beta-cypermethrin concentrations and distinct sex differences may exist. According to the short-term physiological responses of the C. sasakii adults to beta-cypermethrin, the above mentioned three detoxifying enzymes in female or male moths play a comparatively active role for it and the activities of the detoxifying enzymes were increased at first and then decreased. Different physiological function of female and male moths, as well as the differences in susceptibility to insecticides, resulted in the dosage and sex differences of the C. sasakii adults responses to the sublethal concentrations of the beta-cypermethrin.