The aim of this study was to investigate effect of dietary omega-3 fatty acid supplementation on the indices of in vivo lipid peroxidation and oxidant/antioxidant status of plasma in rats.The plasma thiobarbituric acid reactive substances (TBARS) and nitric oxide (NO) levels, and activities of xanthine oxidase (XO), superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX) were studied in male Wistar Albino rats after ingestion of 0.4g/kg fish oil (rich in omega-3 fatty acids, eicosapentaenoic acid and docosahexaenoic acid) for 30 days and compared to untreated control rats.The rats in the treated group had significantly higher SOD activity (P<0.001), NO levels (P<0.01) and decreased TBARS levels (P<0.05) with respect to controls whereas GSH-Px and XO activities were not significantly different between the groups. None of the measured parameters had significant correlation with each other in both groups.We conclude that dietary supplementation of omega-3 fatty acids may enhance resistance to free radical attack and reduce lipid peroxidation. These results support the notion that omega-3 fatty acids may be effective dietary supplements in the management of various diseases in which oxidant/antioxidant defence mechanisms are decelerated.