Purpose: Mental disorders are a major contributor to the global burden of disease and disability, and can be extremely costly at both individual and community level. Social capital, (SC) defined as an individual’s social relationships and participation in community networks, may lower the risk of mental disorders while increasing resilience capacity, adaptation and recovery. SC interventions may be a cost-effective way of preventing and ameliorating these conditions. However, the impact of these SC interventions on mental health still needs research. Methods: We conducted a systematic review of SC-based interventions to investigate their effect on mental health outcomes from controlled, quasi-experimental studies or pilot trials. We searched twelve academic databases, three clinical trials registries, hand-searched references and contacted field experts. Studies’ quality was assessed with the Cochrane Risk of Bias tools for randomized and non-randomized studies. Results: Seven studies were included in the review, published between 2006 and 2016. There was substantial heterogeneity in the definitions of both SC and mental disorders among the studies, preventing us from calculating pooled effect sizes. The interventions included community engagement and educative programs, cognitive processing therapy and sociotherapy for trauma survivors, and neighbourhood projects. Conclusions: There are paucity of SC interventions investigating the effect on mental health outcomes. This study showed that both SC scores and mental health outcomes improved over time but there was little evidence of benefit compared to control groups in the long term. Further high-quality trials are needed, especially among adverse populations to assess sustainability of effect.