Abstract: Tobacco mosaic virus is an important disease and causes damage on tobacco. Elicitors can induce tobacco systemic resistance against TMV. In this study, a glucan elicitor Gep1 was isolated and purified from the culture filtrate of Phytophthora sp. through the procedures of ethanol precipitation, DEAE-52 and SephadexG-100 column chromatography. Gep1 triggered tobacco defense responses. After induced by Gep1, H₂O₂ and phenolics accumulated more and activities of peroxides, polypheol oxidase and phenylalanine ammonia lyase all increased in tobacco leaves. Gep1 could induce tobacco resistance against TMV. In pot experiment, control efficiency of 4 mg/mL Gep1 was 67.4%. Gep1 could effectively reduce the incidence and delay the onset time. Semi-quantitative RT-PCR data revealed that expression of the resistance-related genes in tobacco was up-regulated after Gep1 treatment. The results suggested that Gep1 could trigger defense reactions, induce systemic resistance and improve resistance of tobacco against TMV.