RationaleDespite the well-established link between an immigrant's destination-language proficiency and psychological well-being, little is known about the relationship between an immigrant's destination-language proficiency and well-being of their children. ObjectiveThis study investigated whether and how immigrant mothers’ Korean proficiency is associated with life satisfaction and depressive symptoms among their children in South Korea. A comprehensive set of potential underlying mechanisms was also examined. MethodsUsing four waves of data from the Multicultural Adolescents Panel Study (MAPS), this study estimated fixed effects regression models to reduce the possibility of bias due to individual-level heterogeneity. To test for mediation formally, Sobel mediation tests were conducted. ResultsFixed effects estimates suggested that immigrant mothers' Korean proficiency is positively associated with their children's psychological well-being. Specifically, a one-standard-deviation increase in Korean proficiency was associated with an increase in life satisfaction by 13% of a standard deviation and a decrease in depressive symptoms by 9% of a standard deviation. Mediation tests revealed that this association is explained by a combination of social-psychological factors. Friend support was the most salient mediator, followed by lower acculturation stress, positive perceptions of local community, and teacher support. ConclusionsThe findings of this study suggest that efforts to improve immigrant mothers' destination-language proficiency would also benefit their children's psychological well-being. Furthermore, promoting children's relationships with peers at school may mitigate the negative psychological consequences of immigrant mothers' limited language proficiency.