PURPOSE: We sought to investigate the association between social capital and child behavior problems in Iwate prefecture, Japan, in the aftermath of the 2011 Great East Japan Earthquake. METHODS: Children and their caregivers were recruited from four nursery schools in coastal areas affected by the tsunami, as well as one in an unaffected inland area (N = 94). We assessed the following via caregiver questionnaire: perceptions of social capital in the community, child behavior problems (Child Behavior Checklist, Strength and Difficulty Questionnaire), post-traumatic stress disorder (PTSD) symptoms, child’s exposure to trauma (e.g. loss of family members), and caregiver’s mental health (Impact of Event Scale-R for PTSD symptoms; K6 for general mental health). We collected details on trauma exposure by interviewing child participants. Structural equation modeling was used to assess whether the association between social capital and child behavior problems was mediated by caregiver’s mental health status. RESULTS: Children of caregivers who perceived higher community social capital (trust and mutual aid) showed fewer PTSD symptoms. Furthermore, caregiver’s mental health mediated the association between social trust and child PTSD symptoms. Social capital had no direct impact on child behavior problems. CONCLUSIONS: Community social capital was indirectly associated (via caregiver mental health status) with child behavior problems following exposure to disaster. Community development to boost social capital among caregivers may help to prevent child behavior problems.