This study investigated the effect of dietary n-6 and n-3 fatty acids on fatty acid profile in tissue and the status of vitamin E and lipid peroxidation, and activities of glutathione peroxidase and superoxide dismutase. Male Sprague Dawley rats were fed for 6 wks six experimental diets containing 11.8% fat (w/w, 25% calorie) which was different only in fatty acid composition. The fats used were beef tallow as a source of saturated fatty acid, corn oil as a source of n-6 linoleic acid, perilla oil as a source of n-3 $alpha$-linolenic acid, and fish oil as a source of n-3 eicosapentaenoic acid and n-3 docosahexaenoic acid. Coconut oil was added to diets to give the total amount of saturated fatty acids and monoenes at similar levels in all dietary groups. With the dietary manipulation, effects of n-6 and n-3 fatty acid on tissue fatty acid profile and the parameters indicating lipid peroxidation status could be observed under the conditions providing 1) the equal amount of fat in diets and 2) similar amount of n-6 or n-3 principal fatty acids (LA, ALA, EPA+DHA) in diets, and 3) varing the degree of fat unsaturation. Perilla oil or fish oil increased the incorporation of c20:5 into liver tissue compared to beef tallow or corn oil and its effect was greater by fish oil. Fish oil significantly increased the incorporation of c22:6 into liver but not by perilla oil. The ratio of 20:4/20:5 was increased by corn oil but decreased by perilla oil and fish oil. Plasma or liver tocopherol level was decreased by fish oil and negatively correlated (p<0.005) to the degree of fat unsaturation. RBC hemolysis was correlated to the plasma malondialdehyde (MDA) level (p<0.05) which was negatively related to liver superoxide dismutase (SOD) (p<0.01) and glutathione peroxidase (GSH-Px) activities (p<0.005) although levels of SOD and GSH-Px activities were not significantly and directly affected by dietary fats. Liver MDA level was affected by dietary fatty acid composition. Fish oil, rich in n-3 fatty acids and high in unsaturation, significantly increased MDA level in liver which was positively related to the fat unsaturation (p<0.005). Overall, the addition of large amount of tocopherol to the highly unsaturated diet could not prevent the lipid peroxidation in tissue which was influenced by the degree of fat unsaturation and was greater by n-3 fatty acids containing fats especially fish oil.