Abstract: Surface markings of aeciospores of three species of Cronartium examined under SEM are characterized by annulate processes with five to seven layers and a welldeveloped smooth area. The three species could he distinguished from one another by the morphology of the processes.The processes of Cronartium flaccidum are more prominently narrowed towards the tips and have more varied shapes and sizes,than those of the other two species.Processes of C.quercuum are gradually narrowed towards the tips,while the processes of C.ribicola are about the same in width from bottom to the tips. Between some near by processes,there are several fibrils connecting the same layer of annulation.