The present study aims to examine the mediator role of postpartum depression in the relationship between mothers' obsessive and compulsive behaviours regarding baby care and breastfeeding self-efficacy. The study has a correlational survey design. The regression analysis method was employed to test the mediator role. A significant negative correlation was identified between mothers' obsessive and compulsive behaviours regarding baby care and breastfeeding self-efficacy. A significant negative correlation was determined between breastfeeding self-efficacy and postpartum depression. A significant positive correlation was revealed between postpartum depression and mothers' obsessive and compulsive behaviours regarding baby care. Postpartum depression was determined to play a full mediator role in the relationship between mothers' obsessive and compulsive behaviours regarding baby care and breastfeeding self-efficacy. An increase in mothers' obsessive and compulsive behaviours regarding baby care will increase postpartum depression and adversely affect breastfeeding self-efficacy.