This study aimed to identify the important training needs for master teachers in secondary schools in the Sultanate of Oman as perceived by supervisors and master teachers. The study attempted to answer the following questions:1. What are the most important training needs for master teachers in secondary schools in the Sultanate of Oman as perceived by themselves? 2. What are the most important training needs for master teachers in secondary schools in the Sultanate of Oman as perceived by supervisors? 3. Are there any differences among the master teachers in the Sultanate of Oman in their perception of the training needs based on their experiences, Jop, qualifications, gender, area and nationality? 4. What are the suggested processes, which may improve the training need assessments of master teachers in secondary schools in the - Sultanate of Oman? The study sample consisted of (243) secondary school master teachers, and (128) supervisors from the five educational areas chosen. To answer these questions, a questioner was prepared. It consisted (63) sections based on (8) different subjects. The most important points the study has concluded are: • According to the master teachers, the study fields were ordered in a descending order as follow: teaching methods, professional development of teachers, assessment and teaching technology, management and supervision, student affairs and communication with local communities. • According to the supervisors, the fields were ordered discerningly as follow: professional development of teachers, assessment and teaching technology, teaching methods, management and supervision, communication with local communities and student affairs. • There are differences at the (a= 0.05) level for all six variables of this study. In the light of these results, the researcher has come up with a set of recommendation to develop the training process of master teachers at service.