This paper is an attempt to explore the interaction discourse of second language undergraduate learners in the online peer review process of a writing classroom in Hong Kong. Specifically, the writer sought to investigate the types of online discourse learners have in the peer discussions on their writing, and to examine the role of explicit instructions and training for producing quality online peer discourses. Finally, she hoped to understand how instructors could better support and facilitate effective online discourse in peer reviews. Ongoing developments in Hong Kong's higher education call for implementation of more innovative technology-assisted teaching methods that emphasize learner autonomy; thus, this study examines online discourse that occurred during the peer review process in a writing class in which learners assisted one another in revising their writing with the help of technology. The study was conducted on a group of first-year part-time undergraduate students in an Early Childhood Education program in Hong Kong. In this paper, the online peer discourse was assessed by examining the types of comments students made for their peers during two writing tasks: a group task and an individual task. To facilitate the analyses of peer responses, a coding scheme was used (Liang, 2008). Results show that students tended to give more positive revision-related comments and that explicit instruction and training had an impact on the quality and quantity of online discourse. In conclusion, the author identifies several essential elements for facilitating online peer response groups.