In facing the current era of globalization, it is necessary to implement an application that supports students to improve their English proficiency. The research aims to investigate the implementation of English as a Medium of Instruction (EMI) in religious subject and students’ voices on their language proficiency development and learning confidence after joining EMI-based class. The researcher used the descriptive qualitative case study method. The subject of the research was 17 students at Maahad Tahfiz Al-Qur'an Darul Falah Selangor, Malaysia. The data were collected through field observation and interviews and triangulated by meta observation and member check. The research revealed the dual role of EMI in improving English language proficiency while facilitating content mastery, despite challenges such as students' varying levels of self-confidence. EMI improved language proficiency. Its effectiveness depends on strategies tailored to support students' diverse needs. These insights contribute to optimizing EMI practices and advancing education policies that align with global academic demands. The integration of language and subject knowledge through EMI prepares students for academic success and equips them with the linguistic and cognitive skills. The recommendation is that further research into the other scope of EMI is needed to explore the long-term impact of EMI on students' academic performance and language proficiency, particularly in diverse educational contexts to serve as a valuable tool for promoting inclusive and effective educational environment.