Abstract: The study of the natural infection of aphid and the insect-resistant assay of transgenic ChIFN-γ tobacco in field verified that transgenic tobacco demonstrated a significant enhancement in insect resistance.To reveal the mechanism of the insect resistance to the transgenic ChIFN-γ tobacco,the content of nicotine in the transgenic leaves was determined and the tissue stained technique was carried out.No significant difference was obtained in the contents of nicotine between the transgene and wild type.However,the leaf thickness,cell density,cell wall thickness of the transgenic tobacco showed an improved trend in the transgenes,which might suggest that these parameters probably contributed to the positive resistance to tobacco aphids and Spodoptera litura larvae.