This research aims to analyze the role of organizational commitment in mediating the influence of work satisfaction in organization toward organizational citizenship behavior (OCB) type I and O. The result of this research is very important for improving the organizational performance, especiallya in developing OCB behaviour amongst the members. Research subject is member of Himpunan Mahasiswa Manajemen (HIMAMA), a student organization in the Dapertment of Management, Faculty of Economics and Business, Universitas Muhammadiyah Yogyakarta. Sample was determined through purposive sampling, yielded 102 respondents. Data was collected using questionnaires analyzed using Structural Equation Modeling (SEM) with AMOS software. The findings show that Work Satisfaction in Organization and Organizational Commitment has a significant and positive influence toward OCB I and O. Work Satisfaction in Organization also has significant and positive influence toward Organizational Commitment. The research confirmed that Organizational Commitment mediates the influence of Work Satisfaction in Organization with OCB, particulary OCB-I, however, it did not mediate Work Satisfaction in Organization toward OCB-O.