The changes in human milk composition from 2-5 days to 12 weeks postpartum were investigated. Milk from 62 mothers was anlyzed for total nitrogen(semimicro kjeldahl) lipid(utilizing a modified Folch) and lactose(enzymatic hydrolysis) Energy was calculated by frac-tional analysis. And the daily milk intakes and major nutrients and energy intakes of 18 exclusi-vely breast-fed infant were determined by the test-weighing procedure and the direct analysis of milk samples at 6 or 7 weeks postpartum. All samples were from well-defined subjects and uniform collection procedures were used. Total nitrogen content decreased significantly from 392 to 211 mg/dl lipid and lactose content increased from 1.94 to 3.06g/dl and 6.90 to 7.50g/dl respectively. And energy content increased 55.6 to 64.5 kcal/dl but was not statistically significant. The amount of milk ingested ranged from 432 to 1266 ml/day and the mean intake was 764 ml/day. Daily mean intakes for protein and energy were 10.0g and 450kcal in 6 or 7 weeks postpartum respectively.