This longitudinal study aimed to examine the role of a professional learning community (PLC) in changing teachers' beliefs and practices. Teachers of a Chinese department in a Hong Kong secondary school were interviewed and observed. The findings indicate that the features of a PLC-facilitating teacher change are development of a coherent structure, a collaborative culture, and effective learning activities. These help teachers to overcome initial difficulties and induce their motivation for transformation. Teacher change in five dimensions (curriculum, teaching, learning, roles of teachers, and learning to teach) and three patterns (change in practice but not in belief, change in belief but not in practice, change in practice and belief) were detected. It is argued that cultivating an effective PLC is significant to teacher development.