This study was to compare the effects of dietary n-6 and n-3 fatty acids and fat unsaturation on plasma lipids and chemical composition of VLDL and LDL fraction and lipogenic enzymes activity in rat liver under the conditions providing 1) a similar amount of n-6, n-3 fatty acids(LA, ALA, EPA+DHA) in diets and 2) the various degree of fat unsaturation. Male Sprague-Dawley rats weighing 420g were treated for 6-n with six experimental diets providing 25% of energy as fat and which were different only in fatty acid composition. The fats used for a source of each fatty acid were beet tallow for saturated fatty acid corn oil for n-6 linoleic acid(LA) perilla oil for n-3 $alpha$-linolenic acid(ALA) and fish oil n-3 eicosapentaenoic acid (EPA) and n-3 docosahexaenoic acid(DHA). Plasma cholesterol level was increased by corn oil to compare with beef tallow but was decreased by perilla oil or fish oil. Plasma TG level was significantly decreased by perilla oil or fish oil. Fish oil significantly reduced the level of HDL-Chol and the proportion of Chol in LDL fraction and that of TG in vVLDL fraction. Overall there was a singificant negative correlation between the level of each plasma lipid(Chol TG, VLDL-TG, LDL-C) and the degree of fat unsaturation. However this rerlationship is not always true when compared the hypolipidemic effect of each fatty acid at a similar level of fat unsaturation. There was a trend such taht glucose 6-P dehydrogenase 6-phosphogluconate dehydrogenase and malic enzyme activites were reduced by n-3 fatty acids. Perilla oil significantly increased the incorporation of c20:5 and c22:5 into liver tissue and fish oil suignificantly increased the incorporation of c20:5, c22:6 into liver tissue and the effect of long chain n-3 fatty acid incorporation was greater by fish oil. therefore the hypotriglyceridemic effect of n-3 fatty acid could be resulted from the interference of hepatic lipogenesis by long-chain n-3 fatty acids and the reduced proportion of TG in VLDL fraction and its effect was greater by n-3 EPA+DHA than n-3 ALA even though plasma Chol and TG levels were also influenced by the degree of dietary fat unsaturation.