Due to globalization, English as a medium of instruction (EMI) has gained popularity in higher education. While EMI is mostly adopted in content courses, content instructors may explicitly or implicitly attend to language to help students comprehend course content. However, little research has explored how content instructors provide language support and its impact on students' learning. Adopting the concept of language-related episodes, this study first identified the foci and strategies of the episodes initiated by an EMI instructor and then investigated the effects of EMI and the episodes on students' academic and vocabulary development. The results indicated that the instructor often focused on disciplinary vocabulary and used code-switching as a strategy. In addition, students showed improvement in academic and disciplinary vocabulary, though EMI seemed only to have a slight and indirect effect on students' academic vocabulary gains. Overall, the findings confirm the importance of language support in EMI courses and call for collaboration between content and language experts in developing effective language support strategies.