Abstract: The size and density of stomata, transpiration rate and activity of peroixase of poplar leaves inoculated with Marssonina brunnea of some poplars in Section Aigeiros were analyzed with the resistance to Marssonina brunnea. The results indicated that there was no relationship between the size and density of stomata, transpiration rate and the resistance, but the activity of peroxidase was closely related to the resistance of poplar. After inoculation with the pathogen (M. brunnea f. sp. multigermtubi) peroxidase activities of all species increased. The increasing levels of the resistant species were higher than that of the susceptible ones. Activities of the enzymes showed two peaks.