Arsenic is toxic to a wide range of organisms including plants. Excessive application of arsenical pesticides in agricultural lands has resulted in elevated levels of arsenic in soils. Studies on arsenate, the predominant form of arsenic in aerobic soils has shown that plant species not resistant to arsenic suffer considerable stress upon exposure. Phytotoxicity of arsenic occurs due to its ability to enter in to biochemical reactions in the place of phosphate. The major symptoms of arsenic stress include growth inhibition, chlorosis, defoliation and water-deficiency stress. Exposure to inorganic arsenic species also results in the generation of reactive oxygen species (ROS) and leads to the synthesis of enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). The objective of this study was to gain insight into the biochemical stress response mechanism in monocots upon exposure to arsenical pesticides. We investigated the effect of increasing concentrations of arsenic on laboratory-grown rice seedlings. Plant response to the addition of phosphate in the presence of arsenate was also studied. Biochemical stress response was studied by monitoring the activities of SOD, CAT and POD enzymes. Inhibition of growth was studied by monitoring root and shoot lengths as well as seedling biomass. The results show increased activity of CAT, POD and SOD for fresh weight and total protein in rice seedlings treated with arsenic. For rice seedlings treated with arsenic and phosphorous, the increased activity of CAT, POD and SOD was seen in the fresh weight but not in the total protein. An increased activity of antioxidant enzymes was found in the shoot than in the root, which indicates that the plants acquired tolerance to arsenic. Uptake of arsenic from root to shoot increased in presence of phosphorous. The importance of antioxidant enzymes in protecting monocots from arsenic stress was evident.