This research explores international English majors' experiences and perceptions of the characteristics of an effective English-as-a-medium-of-instruction (EMI) course. Through an analysis of the triangulated data collected through questionnaire surveys, classroom observations, interviews and correspondences between 45 students and their lecturer in an EMI course at a key comprehensive university in Beijing, this study found that international English majors viewed the lecturer's English proficiency, personality, commitment to students and to teaching, teaching approach, and language use as the major factors contributing to EMI course effectiveness. Meanwhile, these students did not consider their own English proficiency as crucial to the effectiveness of EMI courses, and neither did they expect EMI courses to improve their English ability.