This study explores the correlation between the impact of the Great East Japan Earthquake and the incidence of postpartum depression in Miyagi prefecture, Japan. The design used was a cross-sectional study with self-administered questionnaires, 6-9 months after the disaster. The results showed the prevalence of postnatal women with Edinburgh Postnatal Depression Scale (EPDS) score of ≥9 to be 21.3 %. Multivariate analysis showed that exposure to tsunami (odds ratio, 1.80; 95 % confidence interval, 1.16-2.78) was significantly and independently associated with an EPDS score of ≥9. Postnatal women and their children should be treated as a vulnerable population, and a protective framework must be established to prepare for future devastating disasters.