Increasing pollution especially by automobile exhausts in the urban has evidenced the decline in the environmental quality. These pollutants from automobiles are known to affect the physiology of plants. The effects are most often apparent on leaves, which are usually the most abundant and most obvious organs. The study involved determination of effect of automobile exhausts on biochemical composition of two important trees viz., Polyalthia longifolia and Mangifera indica. The leaves of two plants collected frompolluted and unpolluted areas revealed that major effect of the pollutants is on chlorophyll content. Significant loss of chlorophyll was observed in case of polluted leaves. Studies also revealed that these pollutants result in increase in the phenol content of the leaves and decrease in the ascorbic acid content.