This study examined the roles of action research in the professional development of Chinese language teachers. Participants were a group of Chinese teachers enrolled in a teacher training course. In light of theories and research, participants were guided to reflect on their own teaching beliefs and practice and design a research project about their own teaching. Using a descriptive-explorative design, this study elicited data from multiple sources, including students’ pre-course survey, professional journals, reflective essays, project reports, group interviews, email exchanges with the instructor, and instructor’s field notes. Three categories emerged from the data analysis that reflected students’ gains from the process: a broader conception of research on language teaching and learning, a more sophisticated understanding of foreign language teaching in general and their own teaching in particular, and a learning process of how to be a teacher-researcher. Contributing and impeding factors are discussed and values of teacher research are suggested.