To determine the relationship of psychological well-being and cognitive emotion regulation and breastfeeding self-efficacy in mothers in the postpartum period. The research was designed as cross-sectional and correlational and carried out between 1 November 2021 and 1 January 2022 in the pediatric outpatient clinic of a Medical Faculty Hospital of a province in the Central Anatolian Region of Turkey. Responses from a total of 325 mothers who were in postpartum 1–6 months were analyzed. Data were collected using a Personal Information Form, the Scales of Psychological Well-Being (SPWB), the Cognitive Emotion Regulation Questionnaire (CERQ), and the Breastfeeding Self-Efficacy Scale-Short Form (BSES-SF). The following factors were found to be important associated risk factors that negatively affected breastfeeding self-efficacy in 29% of the mothers (F = 14.536, p <.001): mothers' poor mental health, using self-blaming maladaptive cognitive coping strategy, inability to use positive reappraisal coping strategy, and feeding the baby only formula or both breast milk and formula. Weak and positive correlations were found between psychological well-being of mothers and adaptive cognitive coping subdimensions, and negative and weak correlations were found between psychological well-being of the mothers and maladaptive cognitive coping subdimensions (p <.001). Breastfeeding self-efficacy of mothers in a well psychological state, who can use adaptive cognitive coping strategies, and who exclusively breastfeed their babies is positively affected.