Purpose: The aim of the study was to examine the mental health outcomes of folic acid (FA) supplement use in the antenatal and postnatal periods. Materials and Methods: This descriptive-prospective longitudinal study was conducted between 1 December 2019 and 30 January 2021 in a Family Health Center in eastern Turkey. The study was performed at one week in the postpartum period, at 6-8 weeks in the postpartum period, and at six months in the postpartum period. A total of 162 healthy pregnant women were included in the study. A Personal Information Form, the Beck Anxiety Inventory (BAI), and the Edinburgh Postpartum Depression Scale (EPDS) were used to collect data. Results: While 32.7% (n=53) of the participants used FA supplementation from the pre-pregnancy period and in the first trimester of pregnancy (6 months in total), and 34.6% (n=56) used FA supplementation only in the first trimester of pregnancy. It was determined that 32.7% (n=53) of the participants did not use any FA supplement. Of those who did not use FA, 37.0% were in the antenatal period, and 50.8% were on the postnatal 6-8 days. It was determined that the participants experienced mild/moderate/severe anxiety in different weeks. BAI and EPDS scores were the lowest in the prenatal period, at 6-8 weeks in the postpartum period, and at 6 months in the postpartum period in those who used FA supplementation for 6 months. BAI and EPDS scores decreased significantly from the antenatal, to the postnatal 6-8-week, and to the postnatal 6-month measurements. Conclusion: The use of FA supplements can be effective in preventing symptoms of anxiety and depression in the antenatal and postnatal period.