This study was conducted to compare the effects of perilla oil or corn oil on lipid peroxidation and eicosanoid productions which are associated with the promotion of carcinogenesis. in liver or blood in rats. Male Sprague-Dawley8 weaning rats were fed on semisynthetic diets containing 15%(w/w) beef fat(BF). corn oil(CO) or perilla oil(PO) Three weeks after the half of rats in each diet group were injected with a single dose of 50mg 2-acetylaminofluorene (AAF)/Kg BW hepatocarcinogen intraperitoneally 3 times at 2-day interval and all of the rats were sacrificed after 8 weeks from the first injection. The rats fed on different dietary fats without 2-AAF treatment had not different MDA produc-tion and conjugated diene content in liver microsome. CO+AAf group had significantly higher conjugated diene content than BF+AAF and PO+AAF groups. and lower glucose-6-phospha-tase activity than BF+AAF group But PO+AAF had similar conjugated diene content to BF+AAF group and significantly lower MDA production than BF+AAF and CO+AAF groups. The hepatic mocrosomal lipid peroxidation was slightly greater in CO group than in PO group though perilla oil(P/S=9.67) has much more polyunsaturated fatty acids than corn oil(P/S=2.92) PG E2 level in liver and TX B2 level in plasma were significantly higher in CO group than in BF and PO groups. TX B2 level was lowered in CO and BF groups by 2-AAF treatment. These results reach to the contclousion than the type of dietary fatty acid as well as the P/S ratio has effect on hepatic microsomal lipid peroxidation and eicosanoid production and perilla oil or linolenic acid(n3) might be less effective on lipid peroxidation or PG E2 and TX B2 mediated tumor promotion than corn oil or linoleic acid(n6).