In this study, the oxidative damage of α-terthienyl (α-T) to the Spodoptera litura (SL) cell and its mechanism were investigated. MTT was used to compare the toxicity of α-T and rotenone to the SL cell. The output of malondialdehyde and relative content of glutathione were determined with 2-thiobarbituric acid (TBA) and 5, 5′-dithio-bis (2-nitrobenzoic acid) (DTNB), respectively. Transmission electron microscope (TEM) was employed to observe the influence of α-T on the membrane and organelle of the SL cell. The result showed that the IC50 value of α-T to the SL cell was 0.21 μg mL-1, whereas the corresponding dose of rotenone was 12.25 μg mL-1. The output of MDA had the same changing tendency with the concentration of α-T, whereas the content of GSH had the negative correlation with it. According to TEM, the cell membrane and karyotheca swelled and couldn’t retain integrity, the intracellular substances leaked out, unidentified granules appeared in the SL cell. The mitochondria expanded, and the membrane and subcellular organelle were damaged severely. In this study, it was found that after oxidative damage induced by α-T, the output of MDA increased notably, whereas the relative content of GSH decreased. This indicated that the antioxidant ability of cell weakened. The result of TEM implied that the SL cell suffered from oxidative damage under the appointed dose. In this study, the oxidative damage of α-terthienyl (α-T) to the Spodoptera litura (SL) cell and its mechanism were investigated. MTT was used to compare the toxicity of α-T and rotenone to the SL cell. of malondialdehyde and relative content of glutathione were determined with 2-thiobarbituric acid (TBA) and 5,5’- dithio-bis (2-nitrobenzoic acid) (DTNB), respectively. Transmission electron microscope (TEM) was employed to observe the influence of α-T on the membrane and organelle of the SL cell. The result showed that the IC50 value of α-T to the SL cell was 0.21 μg mL-1, while the corresponding dose of rotenone was 12.25 μg mL-1. output of MDA had the same changing tendency with the concentration of α-T, whereas the content of GSH had the negative correlation with it. According to TEM, the cell membrane and karyotheca swelled and could not retain integrity, the intracellular substances leaked out , unidentified granules appeared in the SL cell. The mitochon dria expanded, and the membrane and subcellular organelle were damaged severely. In this study, it was found that after oxidative damage induced by α-T, the output of MDA increased less than, but the relative content of GSH decreased. ability of cell weakened. The result of TEM implied that the SL cell suffered from oxidative damage under the appointed dose.