Rice blast, caused by Magnaporthe oryzae, is the most devastating fungal disease in the rice-growing world. Between 10% and 30% of the annual rice harvest is lost due to infection by rice blast. Mutant plants with altered response to pathogens, either gain or loss of resistance, are useful for dissecting defense mechanisms. For this purpose two rice genotypes including mutant variety Pooya (resistant) and its wild-type cultivar Mosatarom (susceptible) were used in greenhouse tests. Enzyme activities of catalase (CAT), peroxidase (POX), polyphenol oxidase (PPO) and malondialdehyde (MDA) levels were evaluated at 1, 2, 3, 4 and 5 days after inoculation with M. oryzae and the seedlings treated with sterile water was used as control. While enzyme activities of CAT, POX and PPO in the mutant variety Pooya were significantly more than Mosatarom cultivar. Analysis of MDA levels also revealed distinct differences between two genotypes. According to our results, resistance to rice blast in mutant variety Pooya might be associated with modification of antioxidant enzymes activation and membrane lipid peroxidation.