This research aims to examine the mediation effect of teaching behaviour in the relationship between teachers' transformational leadership practices and students' interest in science. A non-experimental quantitative approach was used, with a total of 250 students from secondary private schools in Malaysia participating voluntarily as respondents in the study. Google Form questionnaires were distributed through email for data collection. The findings indicated significant positive associations between teachers' transformational leadership practices, teaching behaviour, and students' interest in science, as revealed by correlation and regression analyses. Mediation analysis demonstrates that teachers' teaching behaviour partially mediates the relationship between transformational leadership and students' interest in science. This study emphasizes the importance of effective teaching behaviour in fostering students' interest in science, providing valuable insights for educational policymakers, school administrators, and teachers in promoting science education and improving students' academic achievement.