Purpose: This study aimed to compare breast milk minerals between mothers with gestational diabetes mellitus (GDM) and healthy mothers. Methods: This study was a short-term prospective study to determine the difference in milk minerals of 30 GDM mothers and 30 healthy mothers. Mineral concentrations in breast milk were measured for Na, K, Ca, Mg, and P. The first breast milk was collected on the 5th day after childbirth, while the second one was collected on the 14th day. For the variation of mineral content of breast milk over time between groups, generalized estimation equations were used. Results: The mean age of the GDM group and healthy mother group was 32.56 and 31.17 years old, respectively. Na was significantly higher in GDM mother group (Wild χ2= 4.35, p= .037) over time (Wild χ2= 21.59, p< .001), and Ca was significantly higher in healthy mother group (Wild χ2= 1.77, p= .018) over time (Wild χ2= 19.09, p< .001). Mg, P, and K showed a significant difference in time (Wild χ2= 18.12, p< .001; Wild χ2= 7.73, p= .005; Wild χ2= 7.10, p= .008). P was significantly higher in GDM mother group on 5th day of delivery (t= 2.08, p= .042). Conclusion: There was a difference in the mineral composition of breast milk between GDM mothers and healthy mothers. Therefore, it is necessary to develop and apply intervention programs such as effective prenatal blood sugar management and postpartum breast massage considering the characteristics of GDM mothers.