The study focused on the extent to which supervision of instruction can determine teacher’s competencies in secondary schools in Ogoja education zone, Cross River State, Nigeria. Four (4) hypotheses were formulated to guide the study and relevant Literatures reviewed. A mix of descriptive and correlational survey design was adopted with a sample size of one hundred and sixty three (163) teachers chosen from ten (10) secondary schools within the zone. A twenty six (26) items questionnaire, tagged-SWOT Analyses Strategic Supervision of Instruction and Teachers’ Competencies Questionnaire was used to obtain data from the field. The data analysis technique used was Simple Linear Regression. All hypotheses were tested at 0.05 level of significance. The results showed that there exist a very high relationship between strength of supervision of instruction and teachers’ competencies, there is no relationship between weakness of supervision of instruction and teachers’ competencies, there is a significant relationship between opportunities of supervision of instruction and teachers’ competencies and also there exist a very high positive relationship between threats of supervision of instruction and teachers’ competencies in the zone. Strategic supervision of instruction is therefore to a great extent a determinant of teachers’ competencies in secondary schools in the zone. Consequently, there is urgent need to reposition the present conventional methods of supervision of instruction to assume the contemporary and scientific approaches for improved student’s achievement in the education zone and to contribute to national development in Nigeria.