Organizational citizenship behavior is a form of behavior that has nothing to do with the formal reward system of the organization, but in aggregate will increase the effectiveness within the organization. Organizational citizenship behavior contained within the organization is able to bring the lecturer to act beyond the task or job that is usually done so as to improve the performance that exceeds the limit. In this study the author examines the organizational citizenship behaviour with aspects that affect the organizational citizenship behaviour, that is transformational leadership and affective commitment. Subjects in this study were Lecturers at Muhammadiyah University of Yogyakarta. Then the number of samples used were 145 respondents by using purposive sampling. The analysis technique used in this research is SEM (Structural Equation Modeling) by using software of AMOS version 22. Based on the results of the analysis, the effect of transformational leadership on organizational citizenship behavior is positively significant, transformational leadership towards affective commitment has a significant positive effect and affective commitment to organizational citizenship behavior has a significant positive effect.