Background and Aim This study aimed to examine the relationship between the postpartum depression levels of mothers and their breastfeeding self-efficacy and perceived social support.<br /> Design This cross-sectional and correlational study was conducted with 180 mothers between October 2022 and May 2023. The data were collected using a "Personal Information Form", the "Multidimensional Scale of Perceived Social Support (MSPSS)", the "Breastfeeding Self-Efficacy Scale-Short Form (BSES-SF)", and the "Edinburgh Postpartum Depression Scale (EPDS)". Data collection took place in the hospital's outpatient clinics and breastfeeding rooms by face-to-face interviews. The data obtained in the study were analysed using the free trial version of the SPSS Statistics for Windows 25.0 program.<br /> Results A statistically significant negative relationship was found between the EPDS and BSES-SF scores of the participants (p < 0.01). There was a statistically significant positive relationship between the MSPSS and BSES-SF scores of the participants (p < 0.01). The BSES-SF and MSPSS scores of the participants significantly predicted their EPDS scores (p < 0.001). It was determined that 43.9% of the total variance in the EPDS scores of the participants was explained by their BSES-SF and MSPSS scores (R = 0.662, R-2 = 0.439). A one-point increase in the BSES-SF and MSPSS scores of the participants corresponded to a decrease of 0.240 and 0.168 points in their EPDS scores, respectively.<br /> Conclusion Increased perceived social support and breastfeeding self-efficacy levels in mothers in the postpartum period reduce postpartum depression. It can be recommended to provide breastfeeding counselling and social support to mothers in the postpartum period.