A total of fifty four 40 day old, male, Japanese quails were fed either a basal diet or a diet containing 15% fat or oil and 2% cholesterol for 3 months. The oils and fats used in this experiment were corn oil, palmitic fatty acids, MCT, coconut and palm kernel oil. No significant difference was noted in the serum triglyceride levels among fat or oil-fed groups. The quails which were fed the diet containing corn oil or palmitic fatty acids and cholesterol showed marked hypercholesterolemia and severe lipid-rich aortic lesions. The quails fed with MCT, coconut, or palm kernel oil and cholesterol had slight increase in their serum cholesterol level and intimal thickening of the aortas. These findings suggest that fats containing abundant medium-chain fatty acids are less atherogenic than the other fats and oils.