Abstract: In order to develop a new type of inhibitors of tobacco mosaic virus (TMV), which is efficient, low toxic and environmentally friendly, silver nanoparticles in quaternized oligochitosan solution was synthesized by using novel oligochitosan derivative with structure of quatemary ammonium salt as reducing agent and stabilizer. Different concentrations of silver nanoparticles in quaternized oligochitosan solution were used to test the resistance against TMV. The results showed that the silver nanoparticles in quaternized oligochitosan solution showed uniform distribution observed under transmission electron microscope (TEM), the particle diameter were mainly 7-12 nm. The best inhibitory effect of silver nanoparticles in quaternized oligochitosan solution to necrosis spots on Nicotiana tabacum cv. Xanthi-nc NN was observed at 25 μ g/mL, with inhibition rate of 74.0%, which was 41.5% and 24.4% higher than that of oligochitosan and ningnanmycin, respectively. On Nicotiana tabacum K326, silver nanoparticles in quaternized oligochitosan solution could relieve the decrease of chlorophyll content, improve the activities of defense enzymes such as superoxide dismutase (SOD), peroxidase (POD) and polyphenoloxidase (PPO) in TMV-inoculated leaves, reduce the content of malondialdehyde (MDA) and accumulate the content of soluble protein. The results suggested that silver nanoparticles in quaternized oligochitosan solution can improve the resistance of tobacco plant against TMV.