The serum concentrations of the major minerals(calcium, phosphorus, magnesium, sodium, potassium) and trace elements(iron, Zinc, copper manganese)were datermined in 23 breast fed infants living in Eumsung, Choong-buk region. The results obtained are summarized as follows: 1)The mean levels of calcium, phosphorus, magnesium, sodium and potassium of the serum of total subjects were 8.15$pm$0.33mg/dI, 11.06$pm$0.16mg/dI, 2.00$pm$0.14mg/dI, 3.4476$pm$17.99mg/dI and 9.06$pm$2.04mg/dI respectively. 2)The serum concentrations of iron, zinc, copper and manganese in total subjects averaged 95.83$pm$0.33mg/dI, 93.79$pm$7.06$mu$g/dI and 98.57$pm$7.06 $mu$g/dI and 4.93$pm$0.62$mu$g/dI respecitively. 3)Breast fed infants had significantly higher serum calcim, magnesium, sodium and iron concentrations than the formula fed groups. Otherwise, serum potassium, copper and manganese levels in breast milk fed infants were significantly lower than those in formula fed infants. 4) In formula fed infants, serum potassium and copper levels increased increased significantly with months after birth.