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Background: Social capital involves a set of norms available in social systems which improves the interaction between people and reduces the costs of interactions and communications. Considering the importance of social capital, this research is aimed to study the social capital and factors affecting it among students of Tehran University of medical sciences.Methods: 400 Students were participated in a cross-sectional study. They were selected randomly commensurate with the student population of each faculty. 36-item Bullen’s questionnaire having 8 dimensions was used for data collection. Finally, for data analyzing were used with SPSS 18 and Independent T- Test, Pearson correlation and regression.Findings: The means of social capital was 44.12. Minimum and maximum mean was measured for “participation in local community” and “family and friends connections” elements, respectively. The study also showed a relationship between social capital with economic status and residencyConclusion: According to the results, there exists a relationship between some dimensions of social capital with economic status, sex, residency and field of study. Authorities could consider these variables and appropriate intervention to increase the social capital of students.