Ample evidence has recognized the importance of teacher support for children's mental health. However, less is known about the factors that may play a role in the association between teacher support and children's mental health. In the present study, we examined the mediating role of self-concept and the moderating role of area (i.e., rural vs. urban area) in the relationship between teacher support and children's mental health (i.e., depression and anxiety). We used a sample of Chinese elementary students who enrolled in grades 3 to 6 (N = 525, aged 8-13, 44.54% girls). Results showed that children who perceived more teacher support tended to report better mental health. Moreover, the relationship between perceived teacher support and mental health was mediated by each domain of self-concept. Lastly, the association between teacher support and mental health was moderated by area, with a stronger effect found for urban children compared with rural children. These findings highlight the importance of considering both individual and contextual factors in the association between teacher support and children's mental health. Practical strategies are proposed for school teachers, professionals, and policymakers to foster children's psychological well-being.