Teacher professionalism has long been a topic of great interest to various stakeholders in education. A review on the extant literature suggested that there were different views on its conceptualization and operationalization. In general, skills and knowledge are two key elements central to the constitution of teacher professionalism. In fact, the definition of teacher professionalism is always changing following new expectations and requirements on teachers, particularly during education reform in a society. These changes may lead to a redistribution of power among different stakeholders in the education system. Teachers are sometimes being empowered but sometimes are being depowered during the changes. In facing challenges coming from the changes, some teachers can get further personal growth and professional development. Over the past decades, Hong Kong has undergone a series of education reforms that exert considerable impacts on teaching profession. In the road of these education reforms, teachers are being empowered through decentralization of decision-making power from central government officials to school-based management. However, this process of teacher empowerment is not monotonous. In recent years, new demands on teaching professionals tend to induce constraints on teachers in exercising their power. The process of teacher empowerment and depowerment in the road of education reform in Hong Kong is a very typical example to illustrate the changing nature of definition of teacher professionalism.