•The social media debate on TCM did not appear to facilitate problem solving.•Users typically communicated only with users who shared their viewpoints.•The debate facilitated the formation of subculture groups in cyberspace.•The study exemplified a plural but fragmented, decentralized but networked public sphere. By analyzing the social media posts published by the scientific community and conventional media organizations, the study explored the recent social media debates on Traditional Chinese Medicine (TCM). A combination of textual analysis and content analysis revealed two main findings. First, different networks of expertise on Weibo generated conflicting discourses about TCM: while the scientific community contributed the overwhelming majority of posts that criticized TCM, conventional media outlets were much more likely to promote TCM without skepticism. Implications of the finding is discussed. Second, the social media debate did not appear to facilitate problem solving, evidenced by the fact that only a small portion of the posts included rational comments about the controversy. In addition, users typically communicated only with users who shared their viewpoints, resulting in few communications between groups. The trend illustrates the fragmentation of China’s networked public sphere on Weibo.