This research intended to answer the question "Is Peer-Assessment on Facebook useful in visual art education?" in an intrinsic case study. Participants were a group of prospective visual-art teachers, who regularly share and comment on the photographs of their paintings in a special group they created on Facebook. Ten volunteering prospective visual-art teachers were involved in the study during 2013-2014 academic year. Focus group interviews were conducted with the participants to collect data in addition to online digital documents, including photographs of students' paintings and comments on them. In general, participants stated that Facebook-based peer assessment is beneficial, since it helps them notice their deficiencies, look at their works from a different perspective and improve their artistic skills. Thanks to the productive feedback, their motivation and self-confidence are boosted. It was also found that peer-assessment on Facebook has the advantage of ubiquity, allowing more peer involvement, easy and objective criticism, and sustainable learning opportunities in the long-run. The participants also emphasized some disadvantages of the practice of peer assessment on Facebook such as subjective feedback and poor quality of digitalized visuals.