We investigated the net photosynthetic rates and antioxidative enzyme activity in Platanus occidentalis trees growing on two separate streets in Seoul, and representing different degrees of air pollution. In general, concentrations, of $SO_2,;NO_2$, and PM10 decreased from May to September. The photosynthetic rate was reduced significantly on the street with higher levels of pollution. Moreover, activities of two antioxidative enzymes, ascorbate peroxidase and glutathione reductase, were greater in May along the more polluted street. These data suggest that P. occidentalis growing in highly p 이 luted environments may increase their antioxidant enzyme activity to compensate for and to minimize the damage from this stress.