Abstract: After COVID 19 pandemic, the government of Kenya, under the ministry of education, enforced regulations which changed the school calendar and restricted co-curricular activities. The purpose of this study was to investigate the impact of students’ involvement in Co-curricular activities on Academic Performance in public secondary schools in Gem Sub County, Siaya County, Kenya. The objectives of the study were: (1) To identify different types of co-curricular activities that learners engage in public Secondary Schools in Gem sub-county, Siaya county, Kenya (2)To assess academic performance of students who participate in co-curricular activities in public Secondary Schools in Gem sub-county, Siaya county, Kenya. This study employed Astin’s theory of involvement, which holds that students learn more when they are involved in both the academic and social aspects of the collegiate experience. The study adopted the concurrent mixed methods design that sought to process the use of both quantitative and qualitative data. The target population of the study comprised of students, co-curricular activities teachers and principals of public secondary schools in Gem Sub County, Siaya County, Kenya. Students were selected through cluster and stratified sampling, while teachers and principals were selected through purposive sampling because it targeted only co-curricular teachers and principals of the selected schools. Simple random sampling was used to select individual respondent. Data was collected through questionnaires for students and co-curricular activities teachers, and interview schedules for the principal. Data was analyzed using descriptive statistics. The study found out that participation in co-curricular activities positively influences students’ academic performance.