With R&D personnel as samples, the purpose of this research is to investigate the effects of transformational leadership, group cohesion and trust on employees’ organizational citizenship behavior. It is found that transformational leadership has a positive effect on group cohesion, trust, and employees’ organizational citizenship behavior. Group cohesion and trust are found to have positive effects on employees’ organizational citizenship behavior. Trust is found to have a positive effect on group cohesion. Transformational leadership is also found to have a positive effect on employees’ organizational citizenship behavior through the mediation of group cohesion. In addition, trust is found to have a positive effect on employees’ organizational citizenship behavior through the mediation of group cohesion. Suggestions and recommendations for future research are discussed.