This study was done to investigate whether dietary fats differing in their fatty acid compositions change hepatic mitochondrial lipid composition and thereby change adenine nucleotide translocase activity. Male Sprague-Dawley rats were fed 5 different wxperimental diets for 6 weeks, which were different in their fatty acid compositions. The dietary fats were beef tallow(BT), olive oil(OO), corn oil(CO), perilla oil(PO) and sardine oil(SO) as a source of saturated fatty acid, oleic acid, n-6 linoleic acid, n-3 $alpha$-linolenic acid and n-3 eiocosapentaenoic acid+docosahexaenoic acid respectively. Body weight of PO group was significantly higher than that of either BT or SO group. This increase in body weight of PO group was due to the increase of food intake. Although there was no difference in liver weight, % liver weight per body weight of SO group was significantly higher than BT and OO groups. Analysis of mitochondrial lipid composition showed that dietary oils differing their fatty acid compositions altered mitochondrial fatty acid patterns, especially n-6/n-3 ratio, cholesterol/phospholipid ratio and phopsholipid composition. The n-6/n-3 ratio was highest in CO group but lowest in SO group whereas the ratio of Chol/PL was highest in SO group but lowest in CO group. Such changes in mitochondrial lipids did not lead to a significant alteration in the activities of adenine nucleotide translocase, which is embedded in mitochodrial inner membrane.