Oxidative stress was induced by in vivo treatment with hydrogen peroxide in rice genotypes showing contrasting behavior to flooding and salt stress. Four rice genotypes FR 13A (Tolerant to flooding stress); CO 43 (Susceptible to flooding stress); FL 478 (Tolerant to salinity stress) and IR29 (Susceptible to salinity stress) were used to study important physiological traits like chlorophyll contents, cell membrane stability, nitrate reductase activity and antioxidant capacity under oxidative stress. H₂O₂ treatments caused degradation in chlorophyll contents, decreased membrane stability and reduced the activities of Nitrate reductase in all the genotypes. A gradual increase in the activities of catalase and peroxidase were recorded under H₂O₂ treatments. Significant upregulation of antioxidant enzyme systems and slow degradation of chlorophyll contents, with less reduction in cell membrane stability and Nitrate reductase activity in the tolerant genotypes (FR 13A and FL 478) play important roles in stress protection.