OBJECTIVE: The goal of this study was to examine the associations of maternal weight status before, during, and after pregnancy with breast milk C-reactive protein (CRP) and interleukin 6 (IL-6), two bioactive markers of inflammation, measured at 1 and 3 months post partum. METHODS: Participants were 134 exclusively breastfeeding mother-infant dyads taking part in the Mothers and Infants Linked for Health (MILK) study, who provided breast milk samples. Pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) were assessed by chart abstraction; postpartum weight loss was measured at the 1- and 3-month study visits. Linear regression was used to examine the associations of maternal weight status with repeated measures of breast milk CRP and IL-6 at 1 and 3 months, after adjustment for potential confounders. RESULTS: Pre-pregnancy BMI and excessive GWG, but not total GWG or postpartum weight loss, were independently associated with breast milk CRP after adjustment (beta = 0.49, P < 0.001 and beta = 0.51, P = 0.011, respectively). No associations were observed for IL-6. CONCLUSIONS: High pre-pregnancy BMI and excessive GWG are associated with elevated levels of breast milk CRP. The consequences of infants receiving varying concentrations of breast milk inflammatory markers are unknown; however, it is speculated that there are implications for the intergenerational transmission of disease risk.