Organizational citizenship behavior (OCB) and social capital are new and inter- disciplinary concepts that have been focused by researchers since 1990s and it seems they have mutual influence. OCB consists of discretionary individual behavior, not explicitly recognized by the formal reward system, which promotes the effective functioning of organization. Social capital refers to relationship and norms that shape the quality and quantity social interaction of society. The importance of these concepts separately encouraged number of researchers of last decades to analyse, demonstrate and make them clear in different aspects. So, present research investigates the impact of OCB on social capital among personnels. In this research, with investigation of OCB literature, six aspects adopted from extractive model of a number of scholars such as: Organ, Graham, Bolino, Smith, Podsakoff, Koopman, Nihef and Mary were used. And in order to study social capital Nahapid and Ghoshal classification were used.The research is measurable-descriptive type that has used library sources, testing theories and Field method in literature review. To do so, a questionnaire of 44 multiple-choice (5 choices) question with Likert spectrum has been gathered of 143 personnels of 5 branches of Shiraz Social Security and analyzed. Achieved results of Piersson correlation coefficient (efficiency) show that there is a meaningful relation between OCB and relational social capital aspects. The results of regression multi-variables analysis show that three aspects of altruism, participation and sportsmanship of perssonels are the strongest predictors of social capital. Also no Significant relation has been seen among social capital and demographic variable such as: age, gender, education, and job experience. According to Freedman test, priority of organizational citizenship behavior aspects is the form of compliance, courtesy, participation, altruism and sportsmanship. And, priority of relational social capital aspects the form of cooperation, trust, commitment, integrity and competence. Also frequency distribution of level of personnel citizenship behavior and social capital show that they are more than middle level in branches of Shiraz Social Security organization. So according to the results, OCB plays an important role in organizational performance by development of social capital.