The present study examined how groupsize may impact students\u2019participation, perceptions, and work quality in an online peer assessment activity. One hundred sixty-three college freshmen were randomly assigned into three conditions that consisted of either 3-student groups, 6-student groups, or 9-student groups. Students reviewed each other\u2019s projects within their groups. Upon receiving peer feedback, students improved their own work. The data analysis suggested that students in bigger groups more actively participated in peer review discussion than students in smaller groups. For students\u2019perceptions, students\u2019responses to SCS and IMI questionnaires did not show considerable differences between the three groups. For work quality, it seemed that students in bigger groups outperformed students in smaller groups