This study was designed to investigate factors that influence girls' performance in physics in (28%) national schools in Kenya, for there is a lower performance index of girls opting to study physics in high schools. The factors of attitudes of students, learners' ability, and teacher characteristics were found to affect performance of girls in physics. A survey among 228 form 2 students in 5 national schools in Kenya, as well as teachers of science and mathematics in the schools was carried out. Questionnaires were used to collect data for both teacher and student factors. In addition, an Achievement Test was used to isolate areas of misconceptions that account for poor performance of girls. The data was analyzed using both descriptive and inferential statistics. The study showed students' attitude, learner's ability and teacher characteristics, affected girls' enrollment and performance in physics. The girls had better positive attitudes and performance in learner abilities in physics than the boys. The results also showed that teachers of physics in the girls' schools are efficient in instructional designs. The results showed strong preference of girls to physics practical work.