Abstract: China’s rapid development and urbanization has induced large numbers of rural residents to migrate from their homes in the countryside to urban areas in search of higher wages. It is estimated that there are more than 60 million left behind children (LBCs) remain in the countryside after their parents migrate. This paper examines the changes in mental health before and after the parents of fourth and fifth grade students out- or return-migrate. We draw on a panel dataset collected by the authors of more than 19,000 students from 252 rural primary schools in northwestern China. Using difference-in-difference and propensity score matching approaches, our results indicate that parental out-migration has a significant negative impact on the mental health of LBCs, as they tend to exhibit higher levels of anxiety and lower levels of self-esteem. However, we find that parental return-migration has no significant effect on the mental health of LBCs.