At all levels of learning and teaching, it is known that teachers play important roles. A teacher’s role may be determined and studied from the functions he performs in different activities. These roles are often stereotyped but under the problem-based learning mode, they are flexible and deserve new studies since the transformation of the teaching and learning model entails a fundamental change of teacher role. As numerous research has been done on teachers’ roles, this paper intends to carry out a literature review of these studies and sort out the possible limitations in problem-based learning environment
