Blended learning is a flexible approach, which with developing technology, assists in the maintenance of education applications both in the face-to-face environment and on the web. The present study was conducted to determine the perceptions of students who took the Computer-Assisted Mathematics Instruction course about the roles and responsibilities of lecturers and students in blended learning (BL) environments; moreover it was aimed to reveal the student opinions about lecturer-student and student-student communication. The opinions of 4th grade mathematics teaching students were obtained using a semi-structured questionnaire containing open and close-ended questions developed by the researcher and a scale to assess the students' satisfaction with BL environments. The students stated their opinions about leadership, guidance and modeling roles of lecturers who gave lessons in BL environments. Engaging the students in the topic were cited among the responsibilities of lecturers. When their opinions about roles and responsibilities in BL environments were examined, it was observed that the students were aware of their responsibilities for their own learning; they were active and would research a topic; they had a questioning approach to their studies, and they worked hard.