This study aimed at exploring and analyzing the effects of peer-review on 7th graders’ motivation and writing performance in composition. This research applied an action research methodology using both qualitative and quantitative techniques for data collection. The target subjects of this study were a group of 7th graders in a school where the researcher teaches. In the period of eight weeks of instruction, each student conducted 4 cycles of peer reviews. Two major scales: An Inventory of Writing Motivation and An Inventory of Writing Performance, were adopted in order to measure the shift of students' motivation and performance before and after the experiment. As for the qualitative approach, teaching journals, oral data from interviews, feedback forms, and the students' writings were collected in order to make a comparison with the quantitive results. The findings include: 1.The students held a positive view of peer reviews. 2.Through peer reviews, there was a positive effect on the writing motivation of the students. 3.Through peer reviews, there was a positive effect on the student's writing performance. 4.With the implementation of this action research, the researchers have become more knowledgeable and optimistic about such teaching strategies. Based on the above mentioned results, the author makes several suggestions that can possibly contribute to teaching practices and studies in the future.