Abstract: Students’ academic achievement in Physics is generally influenced by many factors among which are system, student and parental factors etc. This study examined the influence of students’ interest in Physics and class size on students’ academic achievement in Physics. Descriptive survey design with a study sample of 150 S.S.III Physics students were used in this study. Students’ previous examination result and questionnaires were used as instruments of data collection. Collected data were analyzed using Pearson correlation and multiple regression analysis at 0.05 level of significance.