The aim of this study was to examine the impact of watching an educational video on infant crying within 1 week of age after delivery at maternity wards to reduce the prevalence of postpartum depressive symptoms at 1 month after giving birth. The study design was a cluster randomized controlled trial. The intervention hospitals were randomly assigned, stratified by area and function of the hospital. Participants included 47 obstetrics hospitals or clinics out of 150 hospitals or clinics in Osaka Prefecture, Japan. In total, 44 hospitals or clinics completed the trial and 2,601 (intervention group = 1,040, control group = 1,561) caregivers responded to the questionnaire on postpartum depression (response rate: 55.1%). Mothers in the intervention group watched an educational video, within 1 week of age, during hospitalization at maternity wards. Primary outcome in this study was postpartum depression assessed by the Edinburgh Postnatal Depression Scale as 9+ and assessed via questionnaire at a 1-month health checkup. In the intervention group, 142 (13.7%) mothers reported postpartum depression compared to 250 (16.0%) in the control group. Intention-to-treat analysis showed no significant difference in the prevalence of postpartum depression between the groups. However, among young mothers (<25 years), the analysis showed a 67.0% reduction in postpartum depression (odds ratio: 0.33, 95% CI: 0.15-0.72). Watching an educational video on infant crying within 1 week after delivery at maternity wards did not reduce postpartum depression at 1 month after giving birth, but it was effective for young mothers aged <25 years. © 2020 Wiley Periodicals, Inc.