Abstract Objective We examined the effect of breast milk on plasma total antioxidant capacity (TAC), total peroxide (TP), and oxidative stress index (OSI), which are biomarkers of oxidative status. Methods Fifty-four healthy term infants 3 to 6 mo of age were fed breast milk or a cow’s milk modified formula. Plasma TAC, vitamin C, albumin, bilirubin, and uric acid levels were measured as indexes of antioxidative markers. Plasma TP levels were measured as an oxidative stress marker. The OSI was calculated to assess oxidative status. Results No significant differences were observed between groups with respect to growth or anthropometric measurements. Plasma uric acid, total protein, and albumin concentrations were slightly higher in the breast-fed group than in the formula-fed group. There was a positive correlation between infant’s age and serum albumin levels; between TAC and plasma uric acid, albumin, and total bilirubin; and between plasma iron and TP levels in both groups ( r > 0.256, P < 0.05). In addition, there was a negative correlation between plasma iron and TAC ( r = −0.267, P = 0.01). Plasma TAC and vitamin C levels were significantly higher in the breast-fed group than in the formula-fed group ( P < 0.05). Plasma TP levels and the OSI were higher in the formula-fed group than those in the breast-fed group ( P < 0.05). Conclusions Our data suggest that breast milk provides better antioxidant power than does formula.