Education is an investment whose returns are highly huge throughout the world. Many studies have observed that in most nations, education is increasingly reviewed as a primary means of solving social problems. This study aimed at investigating the factors influencing girls' performance in KCSE examinations in mixed secondary schools in Longisia sub-county, Bomet County. The poor performance of girls in public secondary schools in Longisa sub-county has prompted the study on the factors that have contributed. The research objectives were: determine effect of teaching and learning facilities, teaching methods used by teachers, socio-economic factors attitudes of girls towards class work, and effect of domestic chores on girls' performance in KCSE examinations. The study adopted descriptive survey design and targeted 8 principals, 60teachers and 130 girls in Longisia sub-county. From this target population, a sample size of 8 principals, 60teachers and 130 students were selected. Data were questionnaires, principal's questionnaires teachers' questionnaire, and students' questionnaires. The instruments were conformed valid by the supervisors after pre-testing was carried out by the researcher in three schools outside the study area. From each questionnaire indicated that the questionnaires were reliable in collecting data for the study. Data from questionnaires were them analyzed through descriptive statistics, frequencies and percentages. The findings of the study indicates that parents be sensitized on the importance of quality education and girls be given conducive learning environment at home. More so, needy students were to be provided with bursaries. Established in this study also, was the fact that there is no one factor that is exclusively attributed to the poor performance of girls in KCSE examinations. Factors are varied, one influencing the other. The study recommended that TSC employ more teachers, schools be equipped with adequate learning and teaching facilities and the MOE to re-vamp the bursary kit in schools to sponsor girls from poor families. Above all, a study should be conducted on the role of KESI in empowering teachers and principals in curriculum implementation for quality performance of students in national examinations.