While the study of written discourse that informs ESL writing has provided a number of insights into its conventional features and structures, individual variations such as voice and identity have largely been neglected. To examine how a socially situated notion of voice plays a role in disciplinary online writing, this study explored the co-construction of an author’s identity by peer readers in online written exchanges. The goal of this paper is thus to explore how voice articulated as sociocultural point of view is developed through dialogic interactions with others and how such development can be traced through the discursive constructs such as positioning, epistemic/affective stance, and intertextual relations. This study has important educational implications in relation to academic writing that is a critical issue for many Korean college students who pursue their studies in the United States in that the number of Korean international students has continued to increase in the U.S. universities.