To examine the relationship between maternal prepregnancy weight, gestational weight gain and early introduction of non-breast milk foods and fluids (EINB) in the first month of life, we investigated 592 adult women and their newborns, admitted at health care units in Rio de Janeiro, Brazil. EINB was defined as the introduction of water, tea, juice, other types of milk or food during the first month postpartum. Logistic regression models were used for the analyses. Prepregnant obese women had increased odds of EINB as compared to those with normal weight (odds ratio [OR] = 2.14, 95% confidence interval [CI] = 1.23-3.71). Overweight and obese women who exceeded the recommended gestational weight gain had significantly greater odds of EINB (OR = 2.29, 95% CI = 1.16-4.51, and OR = 3.33, 95% CI = 1.49-7.47, respectively), compared with those with normal weight and adequate gestational weight gain. These findings highlight the importance of providing overweight/obese women with proper lactation guidance in the early postpartum to support for exclusive breastfeeding practices.