This study investigates a group of university teachers' beliefs and practice in using English as a medium of instruction (EMI) in China. Drawing on data from reflective frames and follow-up interviews, the findings shed light on the complexity and multiplicity of EMI teachers' beliefs, which directly shape how they engage in EMI teaching in their respective fields. Specifically, the participants formed different types of beliefs about the roles of English and EMI, about EMI teaching and learning, and about university curriculums and policies on EMI. When they tried to implement their beliefs in practice, they were confronted with a range of obstacles including a lack of professional competence as well as the 'publish-or-perish' culture in higher education. The study argues for a systematic and incremental approach to designing and promoting EMI teaching with subject-specific and community-based support for EMI teachers.