The main purpose of this study is to determine the occupational professionalism of school principals based on the opinions of school principals working in public schools (primary schools, middle schools, and all secondary education institutions). This is a descriptive study in which a survey model was used. The population of the study consists of 387 school principals in the central districts of Kayseri province (Kocasinan, Melikgazi, Talas, İncesu, and Hacılar). The scale was administered to approximately 99% of the population (382 individuals). Data regarding the occupational professionalism of school principals were obtained using the "School Principals' Professionalism Scale". Since the data showed a normal distribution, parametric tests were applied in the study. Inter-group comparisons were made using independent samples T-test and one-way analysis of variance (ANOVA). The statistical analysis was conducted using the SPSS v.23.0 software package. In the study, the school principals’ behaviours regarding their occupational professionalism were examined in the dimensions of professional development, professional autonomy, professional ethics, and decision-making participation. The research results revealed that the occupational professionalism level among school principals was very high. There was no significant differentiation in the behaviors related to school principals’ occupational professionalism based on gender, graduation, total years of service, and years of service in school administration. However, a differentiation was observed in the dimension of decision-making participation. Additionally, it was seen that primary school principals who were previously classroom teachers had higher levels of professional ethical behaviors than school principals in Melikgazi district.