Chemistry is one of the most important branches of science and its contributions to development of a country need to be emphasized. Its performance, however, has been poor especially amongst girls. The purpose of this study was to determine the effect of girls? attitude towards the performance of girls in chemistry in secondary schools in Nandi North Sub-County, Nandi County, Kenya. Descriptive survey research design was adopted. The sample consisted of 303 Form three students and 9 chemistry teachers selected using proportionate, simple random and purposive sampling techniques. Questionnaires, interviews and observation schedules were used to collect data. Validity and reliability of these instruments were determined before data collection. Quantitative data were analyzed using frequencies, percentages and t-test while qualitative data were transcribed and arranged thematically before reporting in narrations and quotations. The study found out that there was a significant difference between boys and girls in terms of attitude towards Chemistry. The study recommended that teachers of chemistry need to encourage and motivate girls to develop a positive attitude toward the importance of chemistry as a subject. The findings of this study could provide a framework for teachers on which they could re-evaluate their instructional strategies during chemistry lessons for the enhancement of effective teaching and learning. It could also provide insight for the curriculum designers into the kind of practical experiences in secondary school chemistry needed to aid sound understanding of scientific concepts and principles.