Women who enter pregnancy above a healthy weight tend to have poorer breastfeeding outcomes compared to healthy weight women. Differences between overweight and healthy weight women’s experience of specific breastfeeding-related problems and reasons for use of formula have not been systematically investigated. The present study compared self-reported breastfeeding problems in healthy weight and overweight mothers and the main reasons reported by mothers for use of infant formula during the first month postpartum. 477 Australian women enrolled in the New Beginnings: Healthy Mothers and Babies Study self-reported breastfeeding problems and reasons for use of infant formula during the first month postpartum. Pre-pregnancy BMI was calculated based on self-reported pre-pregnancy weight and measured height. Binary logistic regression analyses were used to compare pre-pregnancy weight groups (“healthy” [BMI <25 km/m2] and “overweight” [BMI ≥25 km/m2]) on self-reported breastfeeding problems and reasons for use of infant formula. Analyses were adjusted for covariates that differed between groups (P<.1). Frequency of breastfeeding problems was similar across weight status groups. “Not enough milk” was the predominant reason for giving infant formula and predicted breastfeeding cessation. Overweight women were more likely than healthy weight women to agree that infant formula was as good as breastmilk and less likely to agree that medical advice was important in the decision to use infant formula. Guidance regarding indicators of adequate milk supply and the potential risks of using infant formula may be important in supporting exclusive breastfeeding, particularly for overweight women.