Hydrogenated coconut oil or safflower seed oil were fed at 20% levels to weanling male albino rats for 2 months. The fatty acid patterns of the liver homogenates, mitochondria and the microsomes were determined by gas chromatography as were also the fatty acid patterns of the liver cholesterol esters and the phospholipids. The mitochondrial phospholipids were fractionated by thin layer chromatography and the fatty acid moieties of the individual phospholipids were screened on a gas chromatograph. The oxidative phosphorylation in the liver mitochondria was determined using glutamate, malate and succinate as substrates. The liver fatty acid pattern, especially that of the subcellular particles, seemed to be dependent upon the dietary fat. The fatty acid composition of the mitochondrial phospholipids varied with the dietary fat. Oxidative phosphorylation for glutamate and malate was higher in the group fed safflower oil compared to that in the group fed saturated fat; in the case of succinate, no such difference was noticed. These results suggest that the changes in the phosphorylation capacity are due to the changes in the mitochondrial phospholipids which reflect the composition of the dietary fat.