The performance of biology subject in the national examination in Kenya have continuously posted poor results over the years. This study finds out the causes of poor performance in biology in the selected Public secondary schools in Langata Sub-County, Nairobi County. The objectives of the study were to examine the influence of the attitudes towards performance of biology subject, to determine the impact of teaching methods on academic performance in public secondary schools; to evaluate the availability and useof instructional materials in teaching biology and its impact on performance; and to determine future carrier aspirations and it influences on students’ academic performance in biology in Public secondary schools. Questionnaires were administered to students, teachers and interview guide to the principals within the three selected schools in the area. The students were sampled randomly while the teachers and the principals were purposively sampled. The responses were analyzed using Statistical Package for the Social Sciences(SPSS) and presented in figures and tables using percentages. The findings showed that students who have positive attitudes towards biology perform better in the subject while students who have negative attitudes towards biology perform poorly because they lack interest. Classroom participation was poorly managed by teachers and students, majority of the teachers used teachers- centered method of teaching. Most students share biology textbooks which means they are not enough biology textbooks in the schools. The schools did not have adequate instructional materials, they were insufficient laboratory equipment, insufficient teaching and learning materials, amount of content and time allocated were the factors that causes poor performance in biology. Students not interested in biology related careers do not put much effort in biology. Some students are motivated by parents and mentors who work in biology related careers, the study also established that some learners are not aware of their future careers. The study recommend that the Government should provide all the resource material needed for teaching and learning biology such as textbooks, projectors, well-equipped biology Laboratory and Library. Why this recomedation yet this is not in the results and should organize seminar for the learners on career choices, the school administration should frequently organize workshop for biology teachers to upgrade their skills and knowledge regarding teaching and learning of biology. Teachers should always motivate and involved the learners when teaching, they should use variety of methods in teaching biology and to conduct frequent assessments to obtain feedback from the student understanding.