With the emergence of new online technologies and computer-mediated language teaching, many recent studies have been conducted on the effectiveness of online peer assessment. The present mixed methods study examined the effect of online peer assessment on Iranian intermediate-level EFL students` writing accuracy. In the quantitative phase of the study, 28 EFL learners studying in an English institute were randomly assigned to two groups and were taught for 14 sessions. The experimental group attended online peer assessment on Wiki as a forum for out-of-classroom discussions regarding English writing, and the control group attended face-to-face peer assessment. To analyze the numerical data collected through a pretest and a posttest, an independent sample t-test was used to investigate the difference between the two group scores before and after the assessments. The results showed that the difference between the posttest means of the experimental group and the control group was significant. Moreover, the results of analyzing the qualitative data, gathered through focus-group interviews, also confirmed the quantitative results, revealing the positive opinions of the interviewees about the role of technology in language learning. Therefore, online peer assessment seems to have benefits that make it worthwhile despite all the difficulties and extra effort of introducing and teaching it to students. The findings may have implications for material designers, language teachers, and language learners. تفاصيل المقالة