Air pollution occurs when harmful or excessive quantities of substances including gases, particulates, and biological molecules are introduced into Earth's atmosphere. The concept of monitoring of air quality by plants is a well-established fact. It is known that some plants are very sensitive to air pollutants; they are thus used as indicator species for bio monitoring of air quality. The use of lichens and moss for air pollution level mapping in urban and industrial area are the finest examples of plant bio monitoring of air quality. The use of higher plants for monitoring of air pollution is, however, a recent development. A number of plant parameters either simply or in combination may be used for evaluating the pollution stress. Monitoring and detection by instrument cannot be possible everywhere however, indication from plant species by their alterations in morphological and biochemical parameters may be a suitable and easy screening measurement. The present study aims to detect morphological and biochemical changes in leaves of Alstonia scholaris found in Kolkata city area that are exposed to vehicular emission. The results clearly indicate that vehicular load brought significant changes in foliar morphology, numbers of gall formation and biochemical parameters such as pigment content, enzyme activities etc of leaves of A. scholaris. It is concluded that increased Air Pollution Index and gall formation in A. scholaris can be used as early monitoring parameters for air pollution by vehicular emission.