This research investigated the views of lecturers regarding the challenges of teaching English as a medium of instruction (EMI) and its important impact on Thailand International College. A qualitative method was employed utilizing an interview protocol as a research instrument. In total, 12 lecturers from four programs of an international college were selected using a purposive sampling technique. Thematic analysis was applied to examine interview transcripts thus identifying common themes that came up repeatedly. The results revealed that there are four categories of challenges, namely, linguistic, cultural, structural, and identity-related (institutional) challenges and four important aspects of EMI implementation, namely, importance for language improvement, subject matter learning, career prospects, and internationalization strategy. Generally, lecturers found that their students can take notes, read academic texts, interact, and listen through EMI instruction. Taking all of this into consideration, this study provides suggestions for EMI to develop further in Thailand's higher education institutions as all the lecturers have voiced similar positive points on the importance of EMI implementation.