The association between the frequency of eating ready-made meals (RMM) or eating out (EO) during pregnancy and postpartum depression remains unclear. We aimed to explore the association between the frequency of RMM or EO use during pregnancy and the incidence of postpartum depression. This study included 639 community-dwelling pregnant women who were recruited between 2019 and 2022. Data on the frequency of RMM and EO use, as well as sociodemographic, economic and lifestyle factors, were obtained using self-administered questionnaires. Data on dietary intake were obtained using a validated brief self-administered diet history questionnaire. Postpartum depression was assessed using the Japanese version of the Edinburgh Postnatal Depression Scale (EPDS). The incidence of postpartum depression (EPDS score of ≥9) based on the frequency of RMM or EO use was analysed using multiple logistic regression analysis. After adjusting for potential confounders, there was limited evidence suggesting an association between consuming RMM 3 times/week or more and the likelihood of experiencing postpartum depression, with an adjusted OR (aOR) and 95 % CI (95 % CI) of 4·16 and 1·68-10·27 (Pfor trend = 0·017) compared with consuming RMM less than 1 time/week. There was no evidence for an association between consuming EO 3 times/week or more and postpartum depression (aOR: 1·20, 95 % CI: 0·14, 10·04 and Pfor trend = 0·283). Accordingly, the present study presented weak evidence of an association between RMM and postpartum depression. Further studies with large and diverse samples are needed to overcome any potential selection bias.