Role taking is an established approach for promoting social cognition. Playing a specific role within a group could lead students to exercise collective cognitive responsibility for collaborative knowledge building. Two studies explored the relationship of role taking to participation in a blended university course. Students participated in the same knowledge-building activity over three consecutive, five-week modules and enacted four roles designed in alignment with knowledge building pedagogy (Scardamalia and Bereiter 2010). In Study 1, 59 students were distributed into groups with two conditions: students who took a role in Module 2 and students who did not take a role, using Module 1 and 3 as pre and post tests. Results showed no differences in participation in Module 1, higher levels of writing and reading for role takers in Module 2, and this pattern was sustained in Module 3. Students with the Synthesizer role were the most active in terms of writing and the second most active for reading; students with the Social Tutor role were the most active for reading. In Study 2, 143 students were divided into groups with two conditions: students who took a role in Module 1 and students who did not take a role. Content analysis revealed that role takers tended to vary their contributions more than non-role takers by proposing more problems, synthesizing the discourse, reflecting on the process and organization of activity. They also assumed appropriate responsibilities for their role: the Skeptic prioritizes questioning of content, the Synthesizer emphasizes synthesizing of content, and the Social Tutor privileges maintaining of relationships. Implications of designing role taking to foster knowledge building in university blended courses are discussed.