This paper aims to examine the perceptions of teachers and students at a gifted high school in Central Vietnam about teaching science subjects such as Maths, Chemistry, Physics, and Biology through English. Using questionnaires, in-depth interviews, and class observations as research instruments, this study also explores the challenges the administrators, teachers, and students are facing in adopting English as a medium of instruction (EMI). The findings revealed that leaders, teachers, and students appreciate the project and show interest in EMI, but that its implementation experiences a lot of dilemmas and tensions partly owing to English competence, pedagogical methods, materials, and management. From these findings, the study suggests some implications to help make EMI implementation more applicable and effective at the high school level.