%X ANISA LUTFIYANA: The Effect of Leadership of Principal, Organizational Commitment, School Culture on Teacher Professionalism Development of Muhaammadiyah Secondary School of Yogyakarta. Thesis. Yogyakarta: Graduate School, Yogyakarta State University, 2018. This study aims to reveal the effect of: (1) leadership of principal, (2) organizational commitment, (3) school culture, and (4) leadership of principal, organizational commitment, and school culture altogether on teacher professionalism development of Muhammadiyah Secondary School of Yogyakarta. This study is quantitative research. The population was teacher of Muhammadiyah Secondary School of Yogyakarta, as much 280 teachers. A sample of 162 teachers was established using the simple random sampling technique. The data were collected using questionnaire and psychology scale that had been tested for its validity and reliability. The data analysis technique used was double regression applying windows SPSS 22. The results show that there was a positive and significant effect of: (1) principal leadership on teacher professionalism development, as much 15.7%; (2)organizational commitment on teacher professionalism development, as much 15.7; (3) school culture on teacher professionalism development, as much 21.1%; (4) principal leadership, organizational commitment, and school culture together on teacher professionalism development, as much 22%, while the remaining 88% was affected by other factors not included in this study. Keyword: Leadership of principal, organization committee, school culture and teacher professionalism development. %A Anisa Luthfiana %K Kepemimpinan kepala sekolah, komitmen organisasi, budaya organisasi sekolah, pengembangan profesionalitas guru %L UNY74789 %T PENGARUH KEPEMIMPINAN KEPALA SEKOLAH, KOMITMEN ORGANISASI, BUDAYA ORGANISASI SEKOLAH TERHADAP PENGEMBANGAN PROFESIONALITAS GURU SMP MUHAMMADIYAH KOTA YOGYAKARTA %D 2019 %I Fakultas Ilmu Pendidikan