Abstract: In order to develop a new kind of green and high efficiency agent against tobacco mosaic virus (TMV), chitooligosaccharides silver nanoparticles (COS-Ag) solution and chitooligosaccharides schiff base silver nanoparticles (S-COS-Ag) solution were synthesized and tested for their control efficiency on TMV in the field. The results showed that not only COS-Ag solution had good control efficiency on TMV, but also the solution of S-COS-Ag. The S-COS-Ag solution was better than COS-Ag solution. The prevention and treatment effect of S-COS-Ag solution on TMV was up to 53.32% and 24.95% in the field, respectively. The SCOS-Ag solution could inhibit the decrease of chlorophyll content and carotenoid content, with the intensity of photosynthesis enhanced at the same time. As a result, the resistance of tobacco was improved. Therefore, chitooligosaccharides silver nanoparticles (COS-Ag) solution can improve the resistance of tobacco to TMV.