The concentrations of the immunological substances in breast milk and nutritional status were studied in healthy Korean women of middle socioeconomic class. The subjects were recruited at random from obstetric clinics in Seoul. The nutrients intake, prepregnancy BMI, maternal weight gain during pregnancy were studied. The concentrations of lactoferrin(LF), lysozyme(LZ), sIgA, IgG and C3 in colostrum, in transitional milk, and in mature milk, were measured. To elucidate the effect of nutritional status on immunological substances, each components was compared on the basis of either BMI, weight gain, or protein intake. The highest concentrations of the substances were found in colostrum and decreased as lactation progressed. The decline was more prominent in IgG, C3 and sIgA, and less significant in LZ and LF. The colostrum of standard weight gain group showed higher concentrations compared to lower weight gain group. This difference became smaller as the lactation progresses. BMI and nutrient intake status had less significant effect. Lower sIgA was found in lower BMI, in lower weight gain, and lower protein intake groups compared to standard groups, which indicates sIgA is the most affected substance among the measured by nutritional status.