The aim of this study was to examine the relationships between schools' levels of having teacher leadership culture and teachers' professional behaviors. A total of 254 teachers working in primary and secondary schools located in Üsküdar district of Istanbul province participated in the study. The "Teacher Leadership Culture Scale" and the "Teacher Professionalism Scale" were used to collect the research data. The arithmetic mean, Pearson Product-Moment Correlation Coefficient and Multiple Linear Regression analysis were used in the analysis of the data. In the study, schools' levels of having teacher leadership culture and the professionalism characteristics of teachers were found to be above the medium level. Furthermore, significant positive relationships were found between professional cooperation, school administrator's support and the level of having a supportive working environment of the schools' levels of having teacher leadership culture and teacher professionalism. The results of the study revealed that the dimensions of supportive working environment and professional cooperation from among teacher leadership culture characteristics were significant predictors of teacher professionalism. The results of the study were discussed in relation to the relevant literature, and some suggestions were made.