Abstract: This study was conducted to investigate the host plants of the tobacco powdery mildew pathogen in Guizhou tobacco-growing field. Plant tissues with typical powdery mildew symptoms were sampled, pathogens of these hosts were identified by molecular method through analyzing the rDNA-ITS gene of the pathogens, and host plants of the tobacco powdery mildew pathogen were identified by Koch's postulates. The results showed that a total of 36 plant species in 18 different families showed typical powdery mildew symptoms. Among them, the pathogens of powdery mildew in plant species Sonchus arvensis Linn., Helianthus annuus L., Sonchus oleraceus L., Dahila pinnata Cav., Plantago asiatica and Veronica persica were all Golovinomyces cichoracearum, the powdery mildew pathogen of Nicotiana tabacum, which is not the pathogens of the other 30 plant species. After inoculating with G. cichoracearum on host plants, tobacco, V. persica, P. asiatica and S. oleraceus all showed typical powdery mildew symptoms during a 30 days' incubation period, while the other 33 plant species did not. In summary, hosts of G. cichoracearum from tobacco in Guizhou tobacco-growing filed included V. persica, P. asiatica and S. oleraceus.