In this paper, we study relation and impact of social capital on organizational commitment among staffs of Islamic Azad University, Branch of Ayatollah Amoli. The data required were collected by using field (survey) research method and the questionary tool. Statistical population was included 152 subjects that 108 subjects were selected based on Morgan table. The descriptive results show that conditions of independent variables (total social capital, structural social capital, cognitive and communicational social capital) and dependent variable (organizational commitment) are under of average level and this is showing unsuitable conditions. The explanation results showed that all the hypotheses whether the main hypothesis (i.e. the relationship between total social capital and organizational commitment) and secondary hypotheses (i.e. the relationship among structural social capital, cognitive social capital, communicational social capital and organizational commitment) were confirmed. In multiple regression analysis, all variables (i.e. structural social capital, cognitive social capital and communicational social capital) were applied and the effect of them was the significant and coefficient of determination () was 0.406. This shows that independent variables explained 40.6% of the variance and dependent variable variations that is a good value. Also, in order to simultaneously study the direct and indirect effects and all independent variables effects on the dependent variable, the path analysis was used. The variables communicational social capital, cognitive social capital and structural social capital had the most total effect, respectively. The results of this study show the importance, relation, and the effect of social capital on organizational commitment.