The purpose of this study was to identify the effects of principals' transformational headship style on teachers' Altruism organizational citizenship behavior (AOCB). This specific research fills the existing gap in the relationship between these variables. The study included entire Heads and Teachers of Public Sector Secondary Schools in 4 Southern districts of Khyber Pakhtunkhwa as the population. By using L.R Gay's (2003) sample size ratio formula, 8% of the population was selected as samples for the study. For data collection,the first instrument was the Short Form Multifactor Leadership Questionnaire (MLQ) 1995 developed by Bass and Avolio to test the transformational leadership behavior of Heads and the second instrument was the organizational-citizenship-behavior scale (OCBS), produced by Podsakoff & colleagues (1990) to assess the rank of the Altruism citizenship behavior of teachers in Southern districts of Khyber Pakhtunkhwa (KP). The data were organized and the responses to each item were analyzed using relevant statistics. The findings of the study exposed that there is a significant relationship between the Transformational Leadership behavior of Heads and the Altruism Organizational-Citizenship Behavior(AOCB) of Teachers of Secondary Schools in the southern districts of Khyber Pakhtunkhwa (KP) province