This paper reports on an action research project that aims to promote the effectiveness of EMI teaching in a business course. Through systematic reflections and adjustment in her teaching supported by ongoing data collection and analysis, the course instructor identified effective ways to meet students' cognitive and affective needs in EMI classrooms, while she also tried to promote the integration between language and content in her teaching. The paper argues for the importance of action research as a powerful approach to facilitating EMI teacher development in higher education.