Abstract:We found cantharidin having insecticidal activity and synergism with pesticides in previous study. In this paper, the toxicological effect of cantharidin and five insecticides and their mixtures on Plutella xylostella(L.) were determined by leaf dipping method in laboratory to further study the synergistic effect of cantharidin with insecticides and select the synergistic mixtures. The best ratios of different insecticides were ascertained and the combined effect of each mixture also checked. Mixture of cantharidin and abamectin showed additive action with a cooperative virulence index of -1.75. When cantharidin was mixed with endosulfan, chlorfluazuron, bisultap and methomyl respectively according the LC50 value under 1∶ 1,2∶ 3,3∶ 7 and 4∶ 1, CTC values of each mixture were 408.11, 718.97, 216.39 and 414.64 respectively, and all the CTC values were well over 100 obviously, which indicated that cantharidin had different synergistic interaction with the four insecticides and the best mixture is cantharidin with chlorfluazuron.