<b>Challenges Encountered on Capacity Building of Heads of Departments in Public Schools in Kericho County, Kenya</b> The rationale of this study was to investigate influence of capacity building of Heads of Departments on implementation of curriculum in order to improve Kenya Certificate of Secondary Examination KCSE performance in public schools in Kericho County. The performance of KCSE has been decreasing over the last five years 2013—2017 the least mean score being 3.408 which is below average. The study was guided by the following objective namely to establish the challenges encountered by schools on Capacity building of Heads of Departments in order to improve KCSE performance of public schools in Kericho County. The study was used the Theory of Human Capital Theory by Becker and Gerhart 1996 which gave a deeper insight to this research study. The study adopted descriptive survey design which was suitable for this study. The target population was composed of 80 Principals, 400 Heads of Departments and 800 Teachers totaling to 3200. Simple random sampling and purposive sampling was used to get a sample of 1280 respondents. Data were collected using questionnaires and interview schedules. The data obtained was analyzed using Statistical Package for Social Sciences SPSS Version 21 .Both qualitative and quantitative data analysis techniques were used to analyze the collected data which was then presented in form of pie chats, frequency tables and graphs and thematically explained. The study found out lack of time and financial resources for capacity building for Heads of Departments HODs affected curriculum implementation. Majority of the schools held internal seminars to instill efficiency in performance although they had inadequate teachers and incentives. Majority of the respondents preferred the government to sponsor their professional development trainings instead of relying on their already migre salaries. With this in place then there will be success in curriculum implementation through efficiency and effectiveness in learning and performance. In conclusion Principals, Heads of Departments HODs and teachers agreed that they have done very little in full curriculum implementation and professional development leading to poor performance in national exams in subsequent years and other conflicts of interest. The study recommends that the Teachers Service Commission and the Ministry of Education should constantly review its policies to accommodate changing needs of Teachers and Heads of Departments in full Profession Development. Capacity Building, Curriculum, Implementation 82-87 Issue-5 Volume-6 Zeddy Martim