ABSTRACT Aim/Background Both mental maternal health and breastfeeding difficulties impact maternal and infant health. The present study analyses the association between psychosocial and breastfeeding variables and maternal mental health. Design/Methods The participants were 107 first-time mothers from Chile. Sociodemographic variables and breastfeeding difficulties were assessed at 6 weeks postpartum. Depression and anxiety symptoms, parental self-efficacy, and perceived social support were measured using validated, self-report questionnaires at 6 weeks and 5 months postpartum. This study is a secondary analysis of an intervention trial. Results 76% of the women reported having experienced some breastfeeding difficulty in the first postpartum weeks. The number of breastfeeding difficulties was associated with maternal mental health symptoms at 6 weeks postpartum and parental self-efficacy at both assessment times. Women who did not experience breastfeeding difficulties presented significantly fewer depressive (t(102) = 2.5, p = .015) and anxiety symptoms (t(50) = 2.3, p = .028) at 6 weeks postpartum than those who did. Mothers who exclusively breastfed at 5 months postpartum presented significantly higher parental self-efficacy (t(94) = 2.4, p = .044). A higher number of breastfeeding difficulties and low perceived social support contributed to higher depressive symptoms (R2 = .30; F(3,103) = 14.6, p < .001), anxiety symptoms (R2 = .32, F(3.103) = 17.27, p < .001) and lower parental self-efficacy at 6 weeks postpartum (R2 = .39; F(2,103) = 9.4, p < .001). Conclusion Breastfeeding difficulties and social support are associated with fewer mental health symptoms and higher parental self-efficacy during early postpartum in first-time mothers.