Reported was an investigation of the effect of vitamin E (Vit.E) and corn oil on semen traits of male Japanese quail (Coturnix coturnix japonica). From 8 to 20wk of age, birds were raised on corn-based diets supplemented with corn oil (0 and 3%) and Vit.E (National Research Council (NRC) recommended 25mg/kg/day/dry matter and 150mg/kg/day/dry matter) in a 2×2 factorial manner. The diet was supplemented with corn oil and Vit.E (E2C2) which provided additional n-6 polyunsaturated fatty acids in the form of 20:4n-6 and 22:4n-6 in spermatozoa phospholipid. The left testes weights were increased (P<0.01) in groups that received Vit.E in the diet (3.95 and 4.12g, respectively) (P=0.03) and combined testes weight was the greatest in E2C2 group (7.57g) (P=0.02). Semen volume increased throughout the experiment in the E2C2 group. E2C1 and E2C2 birds had the greatest (90.05% and 92.1%, respectively) live sperm percent by comparison with other groups. The susceptibility of semen to lipid peroxidation in vitro was increased in quail fed E1C1 and E1C2, but was reduced when 150mg Vit.E kg/day/dry matter feed was provided in the diet. The amount of Vit.E in the seminal plasma of E1C1 and E1C2 groups was (P<0.01) less than that in the other two groups (E2C1 and E2C2). From this study, it may be concluded that increasing diet n-6/n-3 ratio can be beneficial for semen traits, however, this application increased sperm peroxidation sensitivity but it can be controlled by inclusion of antioxidant such as Vit.E (150mg/kg/day/dry matter) to diet.