Abstract: The aim is to reduce the economic loss of Plasmopara viticola. 19 accessions of Plasmopara viticola from different grapes were collected from different areas in Hunan, Fujian and Jiangxi. The sporangia size was determined, and the differences of pathogenicity in‘Hutai No. 8’,‘Summer Black’,‘Zuijinxiang’,‘Ziqiu Grape’and‘Victoria’were detected. The pathogenic bacteria were cultivated by moisture culture, and then were inoculated to the healthy leaves. The length was detected by sporangium germination method and the pathogenicity was determined by leaf- disc method. The results showed that the size of downy mildew bacterium sporangium from different grape varieties was different. The pathogenic bacteria sporangium from ‘Spine grape’was obviously greater than that of‘Kyoho Grape’and‘Red Earth’. The bacterial strain from Jiangxi had generally stronger pathogenicity, but the bacterial strain from Hunan had generally weaker pathogenicity. European- American cross species grape, such as‘Hutai No. 8’,‘Summer Black’and ‘Zuijinxiang’had relatively low pathogenicity. European-Asian cross species and East Asian species, such as ‘Victoria’and‘Ziqiu Grape’had relative high pathogenicity. The above result indicates that there is a certain differentiation in the pathogenicity and sporangium size of downy mildew collected from different hosts.