The incidence of cardiovascular disease is well correlated with diets high in saturated fatty acids (such as butter). On the other hand, oils, which are rich in unsaturated fatty acids (e.g., sunflower oil and corn oils), reduce cholesterol synthesis and thus show protective effects against arteriosclerosis. However, sunflower oil and corn oil are also considered as risk factors for their sensitivities to free radical formation because of their high contents of polyunsaturated fatty acids (PUFAs). The aim of the present study described herein was to investigate the production of reactive oxygen metabolites (an indicator of oxidative stress) and the activities of several transaminases (markers of hepatic injury) in chick liver treated with highly consumed dietary oils (differing in the degree of saturation). The animals were randomly assigned to six groups of 29 and fed dietary butter, margarine, olive oil, sunflower oil, or corn oil for 2 months. The results indicated that the level of reactive oxygen metabolites (ROM) was lowest in the dietary butter-fed group but highest in the corn oil-fed group. Similarly, the activities of all transaminases measured were lowest in the butter group, and in the margarine-fed group only the Gama-glutamyl transaminase activity was lowest as compared to the control group. From these findings, it was concluded that the dietary butter was the most resistant oil to lipid oxidation, whereas corn oil was the most susceptible one, which may thus challenge the antioxidant defense system and increase the susceptibility of tissues to degradation products of lipid oxidation.