Retraining and upskilling of human resources in organizations are deemed vital whenever a reform takes place, or whenever a huge policy is being implemented on a comprehensive scale. In an education system, officers, principals, and teachers need to be retrained so as to enable them implement and manage new changes, which are manifested in the form of new policies and strategic development plan mooted by the government. This article presents a study on the core professional development needs of school principals in the context of educational reform in Oman since 1998. The study used the survey method in which the respondents comprised 80 principals in Muscat, Oman. The study found fifteen prominent needs factors or domains which were necessary for professional development of school principals in Muscat specifically. The factors apparently could be group into two kinds of leadership needs, namely instructional leadership and transformational leadership. Also, principals contended that a systematic model relevant for professional development programs of principals ought to be designed and used by the Ministry of Education of Oman. New leadership competencies were needed to implement new policies and changes.