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To understand the Eco physiological adaptation mechanisms of Fagus orientalis Lipesk to altitude changes, the activities of Peroxidase (POD), Catalase (CAT), and Ascorbate peroxidase (APX) in leaves of Fagus orientalis in different altitudes (A1: 700 m, A2: 1200 m, A3: 1700 m above sea level)  Was studied in the forests of Guilan. The sampling of leaves was collected from southern and northern parts of the crown of healthy and mature trees. The results of analysis variance showed that there was a significant difference between and within the population for the activity of catalase and peroxidase enzymes at the probability level of 0.05 and with increasing altitude, the activity of catalase and peroxidase were increased but the activity of Ascorbate peroxidase enzyme was initially increased and its level of activity decreased from the middle altitude with increasing altitude. Also, the results showed that the enzymatic activity of peroxidase and catalase in the northern leaves was more than the southern leaves that collected in crown of the trees.