This study aims to investigate the effectiveness of a net-based peer review process for improving Chinese adult e-learners' English writing ability. A class of 36 students participated in this study, which lasted one school year of two semesters. Participants were divided into three groups according to their English writing abilities at the beginning of the study. They attended regular synchronous classes and took writing assignments home. The feature of this experiment is that their writings were submitted for peers' reviews from another group. At the end of each semester, an online writing contest was organized and all the participants took part in order to examine learning outcomes. A survey at the end of the study was also conducted to obtain students' perceptions of the process. The result of the study shows that all the participants obtained satisfactory results, but the students with lower writing ability made more progress than those with higher ability. The finding also indicates that students with higher writing ability tend to become discouraged if they are grouped with lower-ability students for too long.