The purpose of this investigation was to determine the effect of feeding trans fat on serum and tissue lipid profiles and fatty acid composition in mice. Forty-five male mice aged at 4 weeks were fed on the 10% palm oil (n-3 deficient group), 20% dried mackerel (n-3 adequate group) and 5% trans fat (trans group) for three months. Total triglyceride, cholesterol and LDL-cholesterol levels were increased in serum, liver and heart of the n-3 deficient and trans groups compared with the n-3 adequate group, while liver HDL-cholesterol levels were lowest in the trans group (p<0.05). In liver and heart, trans group showed higher levels of total cholesterol and LDL-cholesterol compared with the n-3 deficient group (p<0.05). In fatty acid compositions of serum, heart, liver and kidney, the intake of trans fat led to increased percentages of 18:1n-9trans and 18:2n-6trans. The trans group showed similar patterns to the n-3 deficient group, except an increased percentage of 18:2n-6cis. Generally, the n-3 deficient and trans groups showed increased percentages of n-6 fatty acids and decreased percentages of n-3 fatty acids, specially docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) compared to the n-3 adequate group (p<0.05). These results indicate that intake of trans fat increased total triglyceride, cholesterol and LDL-cholesterol levels, which may affect risk for cardiovascular mortality.