【Objective】Previous studies showed that vetiver grass (Vetiveria zizanioides) can effectively attract female adults of Sesamia inferens (Walker) and Chilo suppressalis (Walker) to lay eggs, while hatched larvae will die after feeding on vetiver grass for a certain time. Therefore, vetiver grass is recommended for field control of rice stem borers. However, the combination of various measures is always used for field control. At present, chemical control is still an irreplaceable measure. Nevertheless, the sensitivity change of rice stem borers after feeding on vetiver to commonly used insecticides is still unclear. 【Method】Seedling dipping bioassay method was used to investigate the toxicity of eight insecticides, including indoxacarb, chlorantraniliprole, spinosad, emamectin benzoate, sulfluramid, metaflumizone, abamectin and chlopyrifos to both S. inferens and C. suppressalis, and the sensitivity changes of these two insect species to these insecticides after feeding on vetiver grass. 【Result】 LC₅₀ to S. inferens were as follows: metaflumizone 1.04 mg/L, emamectin benzoate 1.40 mg/L, chlorantraniliprole 2.67 mg/L, sulfluramid 3.48 mg/L, spinosad 7.59 mg/L, abamectin 13.03 mg/L, indoxacarb 16.57 mg/L, chlorpyrifos 23.28 mg/L; and to C. suppressalis were metaflumizone 1.94 mg/L, emamectin benzoate 2.07 mg/L, chlorantraniliprole 4.20 mg/L, sulfluramid 8.93 mg/L, indoxacarb 9.51 mg/L, spinosad 9.72 mg/L, abamectin 17.63 mg/L, chlorpyrifos 64.68 mg/L. The sensitivity of the two kinds of rice stem borers fed on vetvier grass was increased as compared with the stem borers fed on rice. Three days after feeding on vetiver grass, the sensitivity of S. inferens larvae to eight pesticides was improved, and the mortality was also increased by 13.3%-22.2%. The sensitivities of S. inferens to chlorantraniliprole, spinosad, sulfluramid, metaflumizone and chlorpyrifos were significantly increased, while the sensitivity of C. suppressalis larvae to all the tested pesticides was significantly increased after feeding on vetiver grass with an increased mortality by 26.7%-33.3%. Overall, the sensitivity of C. suppressalis larvae was obviously increased more than that of S. inferens. 【Conclusion】The sensitivity of rice stem borers to eight commonly used insecticides was dramatically increased after feeding on vetiver grass.