The automobile emissions constitute a major source of environmental pollution in Indian cities. Effect of urban air pollution on road side tree species Mangifera indica Linn., Azadirachta indica A. juss., Polyalthia longifolia Benth. et Hook. F. and Cassia siamea Linn. has been studied with special reference to venation pattern of leaves. Effect of air pollution on leaf venation pattern observed at two sampling sites (reference and polluted). The qualitative parameters like primary vein type, course of primary vein, course of secondary veins, inter-secondary vein, marginal ultimate venation, areoles shape, pattern of tertiary veins and type of venation pattern and the quantitative parameters such as length of primary vein in mm, no. of secondary veins along one side of primary, highest degree of vein order, no. of areoles /mm², average size of areoles and absolute veinlets no. in 1000 were examined. The study shows that leaf venation pattern of tree species growing in polluted area were not much affected by air pollution.