Educators show great interest in participating in social-media communities, such as Twitter, to support their professional development and learning. The majority of the research into Twitter-based professional learning communities has investigated why educators choose to use Twitter for professional development and learning and what they actually do in these communities. However, few studies have examined why certain community members remain committed and others gradually drop out. To fill this gap in the research, this study investigated how some key features of online discourse influenced the continued participation of the members of a Twitter-based professional learning community. More than 600,000 tweets generated over six years under the hashtag #edchat were gathered. Online discourse was deconstructed to the cognitive dimension, the interactive dimension, and the social dimension. Text-mining methods were then used to automatically identify these dimensions in the tweets. Finally, survival analysis was used to quantify the influences of these dimensions on users’ commitment time to the Twitter community. The implications of the results and findings are then discussed