To determine the concentrations of fat-soluble and water-soluble vitamins in the maternal milk of Japanese women, we collected human milk samples from more than 4, 000 mothers living throughout Japan between December 1998 and September 1999, and defined as group A the 691 samples among these that met the following conditions: breast milk of mothers who were under 40 y of age, who did not smoke habitually and/or use vitamin supplements, and whose babies showed no symptoms of atopy and had birth weights of 2.5kg or more. We then analyzed the contents of vitamins individually. Large differences were observed among the contents of individual human milk samples. The mean contents of each component were as follows: vitamin A, 159.0±95.2 IU/ 100 mL; vitamin E, 0.325±0.165 α-TE mg/ 100 mL; vitamin D₃ (cholecalciferol), 8.0±10.7 ng/100mL; vitamin B₁ (thiamin), 12.3±3.2μg/100mL; vitamin B₂, 38.4±12.7μg/100mL; vitamin B₆, 5.7±2.5μg/100mL; vitamin B₁₂, 0.04±0.02μg/100mL; vitamin C, 5.1±1.9mg/100mL; biotin, 0.5 0±0.23μg/100mL; choline, 9.2±1.8mg/100mL; folic acid, 6.2±2.9μg/100mL; inositol, 12.6±3.6mg/100mL; niacin (nicotinamide), 32.9±20.4μg/100mL and pantothenic acid, 0.27±0.09mg/100mL. The concentrations of derivatives and/or related compounds of vitamin A (retinol, β-carotene), vitamin E (α-, β-, γ-, and δ-tocopherol), and B₂ (riboflavin, FMN, and FAD) were determined separately. The contents of each were found to vary greatly as the duration of lactation increased. The present results indicate that it is necessary to evaluate individual differences in human milk in order to perform valid research regarding infant formula.