Abstract: In this study the effect of different doses of methylglyoxal (25-400 mg kg-1 body wt.) were examined using enzymes involved in the antioxidant function, superoxide dismutase (SOD), catalase (CAT), glutathion-S-transferase (GST), glyoxalase I (Glyo I) and glyoxalase II (Glyo II) in the liver and spleen of the mice after 6, 12 and 24 h. Significant changes were observed predominantly in the liver. The specific activities of (SOD), (GST), (CAT), (Glyo I), and (Glyo II) were found to decrease in the liver. The mode and magnitude of change in the specific activities were seen to depend on the dose of methylglyoxal and the time of the administration. The present findings suggested of the adverse effect of methylglyoxal on the antioxidant defense system. It is likely that methylglyoxal undergoes a redox cycle and generates the free radicals which in turn lower the antioxidant status in animals.