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. Among the main prominent findings of the study that have been revealed are: 1–According to responses of Teachers 'estimations, the study areas have been listed in a descending order as follows: Follow-up, Planning, Evaluation and Testing, Curricula, Training, Management, School Environment and Local Community. 2 -The sampled Teachers' estimation of the Senior Teacher's role as an Educational Supervisor, as a regular resident in post-basic schools in the Sultanate of Oman has been revealed high in all fields 3- Concerning Gender as a variant ,some significant statistical differences between the estimation of the sample individuals regarding the effectiveness of the the Senior Teacher's role as an Educational Supervisor staying in post basic schools in all fields have been revealed in favour for the female 4–As for Educational Regions, the study also has mirrored, in 2 fields exactly: Management, Evaluation and Testing, some significant statistical differences in the effectiveness of the Senior Teacher's role as an Educational Supervisor dwelled in post- basic schools in favour of Muscat and Dakhilyah whereas the other 5 fields showed no difference ١٧٤ 5–For Subject Matters in all fields, No statistically related significant difference in the sample estimations of effectiveness of Senior Teacher' role as an Educational Supervisor staying in post-basic schools were noticed. Based on this study results, the researcher has presented a number of recommendations and proposals to enrich the effectiveness of the Senior Teacher's role as permanent Educational Supervisor.