In contrast to oral response groups, asynchronous peer review (APR) has received relatively little attention in writing research. This study was motivated largely by the question of whether delayed peer commentary relayed by technology could lead writers to revise writing extensively and improve quality. The purpose of this within-subject, quasi-experimental study was to examine the effect of APR on the quality and revision of argumentative writing. A Web-based program, <u>Calibrated Peer Review^TM</u> (CPR), was used to support the peer review process. Two classes, consisting of 22 students and 16 students, volunteered to participate in this study. After taking the pretest, every participant wrote two argumentative essays and completed a survey. For one essay, participants wrote their drafts and revised their essays alone without APR. For the other essay, the participants completed their drafts, participated in the APR activity supported by CPR, and revised their essays. The treatment, i.e., APR, was administered to the two classes in a counter-balanced manner. Repeated-measure MANOVAs were used to gauge changes over time in holistic quality and the primary traits measured by a revised Toulmin model, and revision changes were coded. This study yielded four findings. First, by holistic quality, the final essays post APR were found to outscore the corresponding initial drafts and the revised essays completed without APR. Second, the final essays post APR were found to outscore the corresponding initial drafts in Claim, Data, Opposition, and Refutation and outscored the final essays completed without the treatment in Claim and Opposition. However, Qualifier did not change at all. Third, extensive surface-based and text-based revisions were produced post APR. Without APR, the participants appeared reluctant to revise. Fourth, the guiding questions used to prompt the peer review process and peer commentary were reported to predominate during the revising process. In conclusion, the entire APR process appears to serve as a catalyst for triggering a great number of surface-based and text-based revisions. Accordingly, revision frequency seems to enhance the holistic quality as well as the four primary traits of argumentative writing.