Flow cytometry (FCM) was used to analysis the destruction of essential oils on membrane integrity of Spodoptera litura cultured cell line SL-1. The cytotoxicity of rotenone and capsaicin alone or in combination with essential oils against SL-1 cells were studied by MTT method. Flow cytometric analysis showed that the intra-cellular fluorescence intensity of accumulation in the membrane impermeable nucleic acid stain propidium iodide (PI) was promoted by 53.04% after 24 h treatment with 50 μg·mL^-1 of rue oil , followed by 34.23% and 33.67% after treatment with angelica oil and turpentine oil, respectively. After being treated with 100 μg·mL^-1 of patchouli oil, turpentine oil, rue oil, angelica oil, citronella oil, and ginger oil, the increase rates of the accumulation of PI were all higher than 40%. The values of median inhibitory concentration (IC₅₀) for rotenone and capsaicin against SL-1 cells for 24 h were 34.97 and 35.92 μg·mL^-1, respectively. When combined with 100 μg·mL^-1 of rue oil, the values of IC₅₀ were decreased to 12.69 and 13.26 μg·m^-1, and the other values were 14.56 and 11.392 μg·mL^-1 when combined with 100 μg·mL^-1 of turpentine oil, which were all lower than those treated with rotenone and capsaicin only. All these results indicated that rue oil and turpentine oil could obviously enhance the cytotoxicity with rotenone and capsaicin.