Owing to to the internalization of higher education, many universities in East Asia provide English as a medium of instruction (EMI) courses for international students. However, previous studies may not have strategically explored the perception of EMI courses for graduate programmes. Recognizing the gap in the literature, this study specifically focused on international graduate students' experiences of EMI courses in a Korean university. By implementing a mixed-method design, this study explored English language learnes’ (ELLs) perceptions of EMI courses regarding i) ELLs’ opinions on the effectiveness of EMI courses, ii) ELLs' attitudes towards EMI, and iii) their self-evaluation of English language ability. Data collection consisted of an end of the semester survey (n=70) and focus group interviews (n=9). The study results showed that i) ELLs showed positive attitudes towards EMI courses; ii) they perceived that the faculty's teaching methods are the core element to EMI course effectiveness; iii) their listening and reading skills were enhanced, and iv) ELLs with low English proficiency found EMI courses challenging to follow. Based on these results, several pedagogical implications are discussed regarding how to implement EMI courses effectively for diverse international students in ELT.