Blended learning has become a popular instruction mode at all levels of education and across different subject areas in recent years. Researchers believe that paradigm shift exists in different domains of blended learning ranging from pedagogy to teacher roles. The present research, thus, used A 27-item and five-likert questionnaire (the STRI) to study how 153 university students perceived the roles of their teachers in both f2f learning and online learning of a blended English course. Statistical analyses revealed two main results: first, all the three sub-roles of teachers in f2f learning had significantly higher means than those in online learning; then in f2f learning, cognitive role had the highest means whereas in online learning, managerial role had the highest means. The findings indicate that, in students' eyes, teachers had greater impact in f2f learning than in online learning. Furthermore, cognitive role of teachers was perceived to be the most impactful in f2f learning whereas managerial role of teachers was regarded as the most notable in online learning. Further comparison of particular items of the questionnaire revealed more specific differences of teacher roles between the two learning modes.