The inducement and time effects of different concentration of methyl jasmonate (MeJA) on peroxidase, polyphenol oxidase, trypsin proteinase inhibitor and chrymoltrypsin proteinase inhibitor in tobacco leaves were studied, and Spodoptera Litura (F.) reared with the studied tobacco leaves was bioassayed. The results showed that the contents of proteinase inhibitors and the activities of oxidases in leaf increased significantly after MeJA spraying; and the relative growth rate (RGR) of Spodoptera Litura (F.) reared with the studied tobacco leaves decreased significantly. 2.4 mmol/L MeJA treatment induced the strongest response in tobacco plant and kept longer.