Abstract: In order to develop new efficient and low toxic biological pesticides against tobacco mosaic virus (TMV), chitosan nano-silver (cos-Ag) and chitosan Schiff-base nano-silver (S-cos-Ag) were synthesized. For investigating their inhibition effects against TMV, lesion experiments were conducted and resistance-related indexes were determined by using Xanthi-NN and Nicotiana tabacum cv. Qinyan96 as the test materials. The results showed that: 1) Thirty-fold diluted S-cos-Ag solution possessed better prevention and treatment efficacies against TMV and significantly reduced the amount of lesions in TMV-infected tobacco leaves, achieving a control efficacy of 78.33% . 2) Thirty-fold diluted S-cos-Ag solution promoted the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and phenylalanine ammonia lyase (PAL) in the tobacco leaves to different extents, leading to increased contents of chlorophyll and soluble protein while decreased malonaldehyde (MDA) contents. These results indicated that thirty-fold diluted S-cos-Ag could induce the TMV resistance on the tobacco and promote its immunity, thereby reducing the harm of TMV to tobacco.