Classroom community in higher education benefits students' learning because it can soothe students' anxiety about isolation. However, only a small number of studies investigated the key factors behind the cohesion of a classroom community. It is a vital issue because previous studies have pointed out that cohesion is crucial for the survival of a community. Against this background, this study developed a research model that incorporates social presence and social capital, so as to identify the decisive factors behind the cohesion of a classroom community. Our research findings demonstrated that social presence plays a pivotal role in affecting the cohesion of a classroom community. The former not only directly influenced the latter, but also affected it indirectly via structural and relational social capital. This result implies that increasing the interaction among community members (e.g. engaging them in discussion rather than allowing them to ignore read messages) is the first priority if we are going to alleviate students' anxiety about isolation with classroom community. As students' interaction increases, their social ties and mutual trust will become stronger, and their cohesion will be strengthened as well.