The present study deals with assessment of response of a tropical soybean cultivar to O 3 in relation to photosynthetic pigments, chlorophyll fluorescence kinetics, antioxidative capacity, N assimilation en-zymes, metabolites, growth and yield using ethylene diurea (EDU) given as a soil drench (400) ppm at an interval of 10 days after germination up to maturity. Mean O 3 concentration was 42 ppb and accumulated threshold above 40 ppb (AOT 40) was 9.07 ppm h. Lipid peroxidation and total phenolics reduced, while increases in activities of antioxidative and nitrogen assimilation enzymes, ascorbic acid, protein, pho-tosynthetic pigments, F v /F m ratio, number of leaves, flowers, pods, branches and yield attributes were found in EDU treated plants. EDU alleviated the negative effects of O 3 by enhancing the first line of defense against ROS and protecting N assimilation enzymes at flowering and maintaining adequate supply of photosynthates to developing pods during pod filling stage. EDU provided maximum protec-tion between flowering to pod filling stage. & Elsevier Inc. All rights reserved.