Migrant women have a higher risk of developing postpartum depressive symptoms (PPDS) than do native women. This study aimed to investigate the role of host-country language proficiency in this disparity. We analysed the data of 1475 migrant and 1415 native women who gave birth at a Portuguese public hospital between 2017 and 2019 and were participants in the baMBINO cohort study. Migrants' language proficiency was self-rated and comprised understanding, speaking, reading, and writing skills. PPDS were assessed using the Edinburgh Postnatal Depression Scale with a cut-off score of ≥10. Multivariable logistic regression models were fitted to estimate the association between language proficiency and PPDS. PPDS were experienced by 7.2% of native women and 12.4% among migrants (p < 0.001). Increasing proportions of PPDS were observed among decreasing Portuguese proficiency levels; 11% among full, 13% among intermediate, and 18% among limited proficiency women (ptrend < 0.001). Full (aOR 1.63 (95% CI 1.21-2.19)), intermediate (aOR 1.68 (95% CI 1.16-2.42)), and limited (aOR 2.55 (95% CI 1.64-3.99)) language proficiencies were associated with increasingly higher odds of PPDS among migrant women, compared to native proficiency. Prevention measures should target migrant women at high risk of PPDS, namely those with limited language skills, and promote awareness, early detection, and help-seeking, in addition to facilitating communication in their perinatal healthcare encounters.