Social capital is as a kind of capital accumulation that causes social solidarity, social commitment and thus improves self-esteem and social health. Erosion of social capital and the turmoil at the macro and micro levels lead to a variety of social and psychological issues and damages. This study aims to investigate the impact of social capital (in-group and out-group) on the mental health of university students in Tabriz and the relationship between the two variables. The method of this study was survey in which statistical population was all students of Tabriz University in three undergraduate, graduate and postgraduate and 300 students by using random sampling method and Cochran formula have been studied. The study is designed to assess the mental health of students using Goldberg General Health Questionnaire (GHQ-28) and the Questionnaire made by the authors. In the present study we used Pearson Correlation for data analysis. The results showed that the there is a positive relationship between social capital (in-group and out-group) and mental health and also there is a significant and reverse relationship between social capital (in-group and out-group) and anxiety, social dysfunction and depression. The study reveals that the social capital (in-group and out-group) has no significant correlation with physical symptoms.