To explore the species of pathogen of leaf rust on black cottonwood ( Populus deltoid e s ) at the south of China, in this study, leaf rust spores were isolated and identified on P.deltoides in JiangSu Province(NanJing,SiHong,SiYang), AnHui Province (HeFei) and HuBei Province (ShiShou). Totally eleven isolates (three in NanJing, four in SiYang, two in HeFei, one in SiHong, one in ShiShou) were obtained by leaf single conidia isolation method. Through scan electron microscope (SEM), the spores of the length, width, thorn distance and diameter of bald surface of each segregation line were found to be largely different between them ( p