This study was conducted to investigate the concentrations and infants intake of sodium and potassium from human milk during the first 5 months of lactation. The sodium concentrations of the milk during the lactation appeared 21.1, 18.1, 15.9, 12.4, 10.6 and 11.4 mg/100g at 0.5, 1, 2, 3, 4, and 5 months of lactation respectively. The potassium concentrations of the milk 48.5, 43.3, 40.8, 39.9, 40.5 and 38.5 respectively, Na/K ratio of the milk were 0.76, 0.75, 0.70, 0.56, 0.46 and 0.53(mEqu\mEq). Sodium intakes of breast-fed infants were 106.9, 108.4, 90.6, 82.5 and 95.6mg/day during the lactation. Potassium intakes of the infants were 255.7, 276.0, 289.7, 294.6, 320.3 and 318.3mg/day. Sodium and potassium concentrations in infant formula averaged 23.62 and 67.61 mg/100g which was 1.90 and 1.69 times as those of breast milk at 3 month of lactation. Commercial whole milks had 39.53 and 135.22mg/100g of sodium and potassium respectively which was 3.19 and 3.39 times as those of the milk. From this study, reevaluation of sodium and potassium intakes if breast-fel infants was merited and the regulation of that minerals in infant formula is need to lower the renal solute load of formula-fed infants.(Korean J Nutrition 34(1):23-29, 2001)