Objective: This study aimed to evaluate the relationship between postpartum depression (PPD) and vitamin D levels in maternal blood and breast milk. Material and Methods: The study included women who presented to a polyclinic between December 2017 andAugust 2018, 4-6 weeks after having given live birth, who were aged between 18 and 40 years and married, gave birth after a planned singlepregnancy, were feeding their baby with only breast milk and stated that they were taking vitamin D supplementation at the dose recommended by the Ministry of Health. The depression status of the women who agreed to participate in the study by signing the volunteer informedconsent form was evaluated using the Edinburgh Postpartum Depression Scale (EPDS). Two groups were formed as Group 1: EPDS score<13 (n=44) (without PPD) and Group 2: EPDS score ≥13 (n=31) (with PPD). The vitamin D levels in breast milk and maternal blood in bothgroups were compared. Results: 75 female patients included in the study had a mean age of 29.80±4.54 years. The mean vitamin D levels inbreast milk and maternal blood were found to be 13.26±5.39 ng/mL and 17.14±6.79 ng/mL, respectively. In terms of depression status, nostatistically significant difference was found between the groups regarding the serum vitamin D levels and the mean level of vitamin D in breastmilk (p=0.463, p=0.847). Conclusion: No significant correlation was determined between the vitamin D levels in maternal blood and breastmilk and PPD, while vitamin D was found to be low both in maternal blood and breast milk.