The purpose of the present study was to assess knowledge levels of school principals about inclusive education at primary schools. For the research, the survey model was applied. The research consisted of 47 school principals employed at 47 primary schools using inclusive education under Kocaeli Provincial Directorate of National Education. According to the study, it was stated that the school principals employed at primary schools with inclusive education did not have sufficient information about inclusion and they did need further information. They did not get any information before inclusive education and did not have enough preparations for the inclusion, they did not get any aid and support in inclusion applications, there were not any special education teachers in inclusive primary schools, inclusive students did not get sufficient supportive educational services, teachers did not sufficiently apply individualised education programs and, therefore, they faced a lack of education materials.