Abstract: Pot cultivation experiments were used to study the effects of Melampsora larici-populina on the physiological metabolism of Populus cathayana under different disease degrees,specifically on the activities of its POD,PPO enzymes,and the contents of its MDA and Chlorophyll.The results showed that the changes of physiological indexes of poplars were closely related with their disease degree.After inoculation with M.larici-populina and with the increasing of disease degrees,POD activity showed a gradient growth and reached its maximum value at the end; As compared with the control groups,PPO activity increased regularly,and there were significant differences with the control (P <0.01);As to chlorophyll content,it decreased significantly in the whole process; While the MDA content decreased slowly after a rapidly increase,and it peaked in the mid susceptible period.The correlation analysis of physiological indexes and disease degrees showed that the activities of POD and PPO were positively related to the disease degree (P<0.05; P<0.01);And the chlorophyll content was negatively related to it (P<0.01); and there was no significant correlation between MDA content and disease degrees.