This research study was tailored to investigate the implementation of instructional supervision and its relationship with teachers’ performance in public secondary schools in Nandi North Sub-County. Descriptive-correlational research design was adopted in which Instructional Supervision and teachers’ Performance Questionnaire were used to obtain relevant data from 187 teachers in 15 selected Public Secondary schools using the simple random sampling techniques. Purposive sampling technique was used to select 42 HODs who were interviewed. Descriptive statistics and Spearman’s rank-order correlation coefficient at 0.05 level of significance were used to analyze the data generated and answer the research questions. The study relied on theory Z by William (1980) which is a supervision model that grew from perceived inadequacies with theories X and Y. Based on TPAD scores the performance of the teachers was above average. The study reveals that the extent of implementation of instructional supervision in lesson preparation, preparation of assessment materials, lesson implementation, and innovation and creativity is good. There is no significant relationship between instructional supervision in lesson preparation (r s = .031, p = .679 > .05), preparation of assessment materials (r s = .132, p =. 072 > .05), and innovation and creativity in teaching (r s = -.036, p = .627 > .05) and teachers’ performance based on TPAD scores. There is a significant relationship between instructional supervision in lesson implementation (r s = -0.152, p = .038 < .05) and teachers’ performance based on TPAD scores. The relationship is weak and inverse, which implies that principals tend to supervise the lesson implementation of teachers whose performance is wanting. One important way of improving instruction is through regular supervision of all teachers by principals of schools and by fully implementing instructional supervision.