Abstract This study investigates the effectiveness of blended learning in teaching English to students at To Ky Secondary School in Ho Chi Minh City. Using a mixed-methods research design, the study examined changes in students’ English achievement, their attitudes toward blended learning, and teachers’ perceptions of its implementation. Quantitative data were collected through pre-test and post-test assessments, while qualitative data were obtained from student questionnaires, classroom observations, and semi-structured teacher interviews. The findings revealed a statistically significant improvement in students’ English learning outcomes after the blended learning intervention. In addition, students reported positive attitudes toward blended learning, particularly in terms of increased motivation and engagement, while demonstrating moderate development of learner autonomy. Teachers also perceived blended learning as beneficial for enhancing classroom interaction and extending learning beyond class time, despite challenges related to learner self-regulation and instructional workload. Overall, the study concludes that blended learning is an effective and feasible approach for improving English language teaching at the secondary school level in Vietnam.