The development of English as a medium of instruction (EMI) has received much attention of language researchers in the era of globalization and internationalization. Despite recognition of problems in implementation, EMI has been widely introduced and applied into higher education in non-native English-speaking (NNES) countries. The question of what challenges face content lecturers in teaching in EMI classrooms is our major focus in this study. The study collected data from 28 content lecturers in EMI programs in a public university in the Mekong Delta, Vietnam. The results from the questionnaire and interview reveal that content lecturers encounter a variation of challenges in EMI classrooms. Specifically, lecturers are challenged by students’ language competence, preparation time for lectures, engaging the class discussion in English and their own language ability. The findings from the study are consistent with the findings of the previous research. Based on these findings, implications are made for enhancing the success of similar programs.