The purpose of this study was to examine the relationship between primary school principals' power styles and teacher professionalism. A total of 264 teachers employed in 10 primary schools in Kastamonu, Turkey, participated in this study. Kosar's (2008) "Power Styles Scale,"and the "Teacher Professionalism Scale"--originally developed by Tschannen-Moran, Parish, and DiPaola (2006), and adapted into Turkish by Cerit (2013)--were used to gather data. The mean, standard deviation, correlation, and regression analyses were calculated to evaluate the data. The results revealed that teacher professionalism was positively and significantly related to personality and reward power, while being negatively and significantly correlated with legitimate and coercive power. The findings also showed that the power styles of school principals significantly predicted teacher professionalism. The outcomes of the study are discussed with respect to improving teacher self-efficacy.