Abstract: 【Objective】 This study aimed to investigate the ability of Vaccaria segetalis extracts in inducing tobacco resistance against tobacco mosaic virus （TMV） to clarify the underlying mechanism， thereby providing a theoretical basis for developing novel botanical pesticides.【Method】 Vaccaria segetalis extracts were prepared and the impact on TMV particle morphology was observed by transmission electron microscopy （TEM）. The preventive， inactivation， and therapeutic effects of the extracts at different concentrations （1.00， 5.00， 25.00， 125.00， and 625.00 mg/L）， together with a control agent （5% amino-oligosaccharin aqueous solution） were determined using the half-leaf local-lesion assay. Pot experiments were subsequently conducted to determine the control efficacy of Vaccaria segetalis extracts at different concentrations and control agent against TMV. Four treatments were established： water spray （blank control， CK）， water spray and TMV inoculation （T1）， Vaccaria segetalis extract spray （T2）， and Vaccaria segetalis extract spray and TMV inoculation （T3）. Defense enzyme activities of tobacco leaves were determined in each treatment.【Result】 TEM observation revealed that the extracts denatured TMV coat-protein subunits and fragmented virions， markedly diminishing viral infecti-vity. Vaccaria segetalis extracts at 625.00 mg/L exhibited the strongest preventive， inactivation， and therapeutic effects on TMV， with the inhibitory rate significantly higher than that of the control agent （P<0.05， the same below）. Throughout the experiment， superoxide dismutase （SOD） activity in T2 and T3 was consistently greater than that in CK and T1； per-oxidase （POD） activity at different time in T3 after TMV inoculation was significantly higher than that in T1； after TMV inoculation， phenylalanine ammonia-lyase （PAL） activity in T3 exceeded that in all other treatments； polyphenol oxidase （PPO） activity in T3 was significantly higher than in T1 on 1 d post-inoculation and remained higher than that in other treatments on 3， 5， 7， and 9 d. When typical mosaic and curling symptoms appeared in the pot experiment， the situation of disease was investigated： 25.00 mg/L Vaccaria segetalis extracts showed the best disease control efficacy （75.50%）， significantly higher than that of control agents.【Conclusion】 Vaccaria segetalis extracts not only disrupt TMV particle structure but also enhance activities of key defense enzymes （SOD， POD， PAL， and PPO）， inducing tobacco resistance against TMV. At appropriate concentrations， Vaccaria segetalis extracts show better preventive， inactivation， and therapeutic effects than the control agent， indicating the extracts have application potential for TMV control.