In the present study we investigated the seasonal pattern of activity of antioxidant enzymes such as superoxide dismutase (SOD) catalase (CAT) ascorbate peroxidase (APX), guaiacol peroxidase (POD) and syringaldazine peroxidase (SPOD) as well as the total protein concentration in the European mistletoe (Viscum album L. subsp. album). We studied mistletoe leaves that grew on the selected tree species in different parts the city of Lodz, exposed to a greater or lesser extent to the nitrogen dioxide. Sampling campaigns were conducted during the growing season 2013 in early May (at the beginning of the growing season) and in November (at the end of the growing season). We showed considerable seasonal variations of antioxidant enzymatic activity and total protein concentrations for all the samples studied. The test parameters varied depending on the host plants exposition to pollution with nitrogen dioxide. The changes in enzymatic activity did not depend on the host plants. In mistletoe leaves greater changes of SOD activity and total protein concentration were observed in autumn. There is correlation between the level of nitrogen dioxide in atmosphere and activities the enzymes. SOD activity was signifi cantly higher in autumn when the host plants were defoliated. Increased CAT activity was observed in late spring. We demonstrated the positive correlation between changes in enzyme activities and the progress of growing season. Increased activities of POD, CAT and APX to a limited extent depended on the place of growing and exposition to air pollution. In late spring activity of the enzymes did not signifi cant grow because of the protective umbrella from host plant leaves preventing the access of nitrogen dioxide to mistletoe. The higher SOD activity in mistletoe is a consequence of oxidative stress causes by nitrogen dioxides evidently observed in the city center. The test parameters, mainly the activity of SOD, can be used in the future as markers of the environment purity, especially in the autumn and winter when the temperatures are above freezing, and there are no leaves on the trees.