This study explores how two language teachers constructed and reconstructed their professional identities through their action research (AR) facilitated by university researchers in China. Informed by the theory of 'community of practice', the findings of the study show that AR exerted a transformative impact on the teachers' identity development. Four distinctive routes of identity change were noted, namely their transformation from "fisherman" to "fishing coach", from "craftsman" to "teacher researcher", from "lonely fighter" to "collaborator", and from "housekeeper" to "change agent". Such change can be attributed to their engagement and practice in different communities of practice. However, the participants' identity development also encountered some contextual obstacles, including the rigid school curriculum, lack of research knowledge, as well as the power dynamics between them and the researchers. Several implications can be drawn for teachers, teacher educators, and school leaders to help teachers construct a solid and robust professional identity in seeking their continuing professional development through AR.