The aim of this study was to explore the relationships between science self-efficacy, gender, and academic achievement in genetics among form four (12th grade) students in Kenya and to investiPSTe gender differences in science self-efficacy and academic achievement in genetics. A total of 2,139 students responded to a science self-efficacy questionnaire, adopted from SEMLI-S by Gregory Thomas, David Anderson, and Samson Nashon (2007). A (PST) was then administered to test the academic achievement of students. Data were analysed both descriptively (means and standard deviations) and inferentially (MANOVA and Pearson's Correlations). Results of the analyses revealed that students' science self-efficacy is highly correlated to academic achievement. One-way MANOVA results indicated gender differences in both self efficacy and academic achievement, with female students performing better than male students in both outcome variables. These findings are inconsistent with the extensive research done on gender differences where females always perform poorer than males in science-related courses and tasks and hence have pertinent implications for both biology teachers and science educators.