Case: A 27-year-old, gravida 2, para 0, Japanese female who was maintained on zinc acetate (75 mg/day) during pregnancy expressed her desire to breastfeed after birth. We investigated the possibility of breastfeeding while on treatment. Breast milk zinc concentrations were determined using an atomic absorption photometer. Breast milk zinc concentrations on the 4th (colostrum) and 32nd (post-colostrum) days post partum were 10.80 μg/mL and 3.28 μg/mL, respectively. These values are less than the reported range of breast milk zinc concentrations in Japanese women who are not under any medication. Conclusion: We measured blood and breast milk zinc concentrations of a patient with Wilson's disease who was taking zinc acetate (75 mg/day). Zinc values were within the range of breast milk concentrations of mothers who are not on zinc acetate.