Objective of this research is to test the effect of transformational leadership, personality and group decision making to Organizational Citizenship Behavior (OCB) to 260 public school teachers selected by using proportional random sampling out of 20 Junior High Schools in Lampung province, Indonesia. Quantitatively and qualitatively through Sequential Explanatory Design, the research concludes that OCB is positively and significantly affected by transformational leadership, personality and group decision making counted of 52,7% (R2 = 0,527, a = 0,01%) revealing other 47,3% to influence OCB. Qualitative finding strengthens the existence of other factors affecting OCB. The research brings implication that to boost teachers' OCB, the school principal must enhance the transformational leadership skill through developing capabilities in strategic planning and change management