This study reports on the perspectives of a group of Iranian EFL teachers about peer observation effects. The aim was to investigate if peer observation as a reflective tool could significantly affect EFL teachers' professional development. It has been done based on a mixed method approach. The participants have stated their viewpoints on the effects, benefits, and weaknesses of peer observation by means of a peer observation questionnaire. Finally, it has become obvious that peer observation as a reflective tool could significantly affect on EFL teachers' professional development; or it has played a significant role in improving EFL teachers' professional development.