The present study investigates the effects that Facebook-based online peer assessment with micro-teaching videos can have on attitudes toward peer assessment and perceived learning from peer assessment. The study recruited a sample of 31 university students who were enrolled in a teacher-training course. Using assessees' microteaching videos, the experimental group performed two rounds of online peer assessments targeting teacher performance; by comparison, the control group performed two identical rounds of peer assessment, but without the assessees' microteaching videos. The results show that the two groups experienced significantly positive changes in attitudes toward peer assessment over time. Moreover, the experimental group's perceived learning about teaching competency was lower than the control group's after completing the first-round peer assessment, but significantly increased over time. Finally, the open-ended responses show that participants regarded Facebook as a convenient tool for performing peer assessments, but voiced their concerns about Facebook's open and non-anonymous features.