This study aimed at investigating the degree of practice of the principal for his / her role in the professional development of basic education teachers in the Sultanate of Oman, from the point of view of both principals and teachers, indicating the impact of the gender, the educational district, years of experience in administration, the scientific degree, and the kind size of school on the points of view of principals while performing this role. To answer the questions of this study, the literature related to the role of the principal in professional development of teachers has been analyzed, then a questionnaire of (44) items categorize into seven domains of professional development has been prepared. The questionnaire was subjected to face validity and reliability tests as it was examined by a number of specialists and checked against (Alpha Koronbagh) laboratories, where the total reliability reached (0,95). A random sample consisting of (237) principals, and (1985) male and female teachers in four educational districts was selected. The results of this study were: 1- According to principals; they estimate that they practice their roles in the professional development of teachers at a high level, but teachers think that it is average. 2- A statistical significant discrepancy was observed between principals and teachers, in most fields of professional development, except for matters related to providing circulars and resource books. 3- Statistically significant differences were observed between principals' and teachers' points of view about the principal's estimation of his role in the professional development of teachers; as the principals' estimation to the degree of their practice was higher than the estimation of teachers to the principals practice. 4- Statistically significant differences were not observed between the estimations of principals about the degree of practice of their roles in teachers' professional development, something which might be due to the variable of the number of years of experience in administration, the variable of the scientific degree and variable of the size of the school, except for the field of (developing teaching skills) for the schools of less than (800) students, and also the variable of the educational district except for the field of (exchanging information and expertise) between the districts of Muscat, Al-Batina North, Al- Dakhlia, and Al-Sharqia South in favour of Muscat Governorate and Al-Batina North and Al-Dakhlia. 5- Statistical significant differences were found between principals' point views about the degree of their practice of their roles in teachers' professional development, which might be due to the variables of gender in favour of females except for the domain of (providing circulars and resource books), and the type of school in the fields of (developing teaching skills, study and research, and exchanging information and expertise) in favour of the principals of basic education schools cycle one (1-4). 6- That the most important difficulties crippling the principal from playing an effective role in professional development are: heavy duties and growing office and administrative burdens. The least of which is weak coordination and cooperation between the principal and supervisors. The researcher recommended more attention to be given to the principal in his / her role in teachers' professional development, and clearing all the obstacles hindering him from doing so.