Breast milk contains bioactive components that contribute to newborn development. However, colostrum may undergo biochemical and immunological changes as a function of maternal overweight and obesity. To investigate this hypothesis, this study determined the levels of hormones and immunological markers in the serum and colostrum of overweight and obese mothers. Colostrum and serum samples were collected from 15 normoweight, 15 overweight, and 15 obese women for determination of leptin, adiponectin, cytokines (TNF-α, IL-6, IL-10), and C-reactive protein (CRP). Obese mothers exhibited higher levels of serum TNF-α, IL-6, and CRP, serum and colostrum leptin and colostrum adiponectin and lower levels of serum adiponectin. Leptin levels in maternal serum and colostrum were positively correlated, as was pre-pregnancy BMI and serum TNF-α, IL-6, CRP, and leptin. Adiponectin levels in colostrum and serum were negatively correlated. The results suggest that obesity changes hormonal and immunological components of maternal serum and colostrum. The modifications can have short-term and long-term effects on newborn development. © 2016 BioFactors, 43(2):243-250, 2017.