Mathematics plays a vital role in many areas of an individual's life. In spite of the role mathematics plays results of the Kenya Certificate of Secondary Education examinations have revealed that although mathematics is a compulsory subject it is one of the poorly performed subjects. Available literature indicates that little has been done to study the role of self-efficacy on mathematics performance in Kenya's secondary schools. The purpose of this study therefore was to establish the influence of self-efficacy on mathematics performance among students in selected public secondary schools in Gilgil Town, Nakuru County, Kenya.The study used an ex-post facto research design and selected 320 students who were randomly selected from 32 public secondary schools in Gilgil town. The target population was form three students. Stratified random sampling was used to get three strata's based on girls only, boys and mixed schools.The study used the SPSS version 22.0 to analyze the data collected.The study established that self efficacy influencing factors which includes; student's social-culture, gender and motivation influences the performance of students in mathematics.