This study targets to explore effectiveness of the Senior Teacher's role as an Educational Supervisor residing in post-basic schools in the Sultanate of Oman. It has tried to find answers to the following questions: 1 To what degree is the effectiveness of the Senior Teacher's role as an Educational Supervisor residing in post-basic schools in the Sultanate of Oman? 2-Are there any differences bearing statistical significance in the Senior Teacher's role as a domicile Educational Supervisor in post -basic schools in the Sultanate of Oman that are attributed to variants of Gender , Educational Region or Subject-matters ? The case study sample was made up of (379) female and male teachers working in MOE, Oman post -basic schools in different educational regions namely: Muscat, Al Batinah North, Al Batinah South and Dakhilyah. A questionnaire, classified into 7 fields of the Senior Teacher's roles specifically: Planning, Management, Evaluation and Testing, Curricula, School Environment and Local Community, Training and Field Follow -ups, has been set up by the researcher in order to probe the above mentioned questions. It has 54 roles played by the Senior Teacher.