Research on microblogging in education has suggested its potential to promote community building and collaborative learning, but little is known about the nature of interaction in such microblogging communities. More research is needed to understand how online learning communities can be designed in a way that supports effective learning. The purpose of the study is to explore how people interact in a popular microblogging-based learning community by examining a one-hour synchronous chat event and analyzing its network structure, levels of participation, major topics generated and types of interaction. The findings suggested that the levels of participation in the synchronous chat were largely uneven. During the chat, participants were engaged in many types of interaction and discussed a variety of issues related to the topic. Interestingly, people who were different in their levels of participation also varied on the types of topics generated, but not on the types of interaction.