The central problem of this study was that despite the critical role played by the principal in secondary school management, students’ academic performance has persistently been poor. Factors leading to this dismal performance have not been adequately investigated and well understood, hence hindering national development in the country. To this end, the purpose of this study was to determine the impact of the leadership behavior of the Principal on the Students’ academic performance in Kenya Certificate of Secondary Education (KCSE) in selected secondary schools in Manga Division, Nyamira District. The study was conducted in eleven secondary schools within Manga Division, Nyamira District. Eleven Principals and 61 teachers from these sample schools were used in the study. The interest for the researcher to choose and study these schools was strongly prompted by their continued poor performance in KCSE. Data was collected using questionnaires and interview schedules. The study used descriptive statistics such as percentages and frequencies, which were used concurrently with the ANOVA test in the analysis. The study was intended to come up with policy guidelines that will help improve the leadership behavior of principals in Kenya and other developing countries, which require similar policies. The study will further contribute to the functions of knowledge for the present and future scholars.