Background: In order to introduce regulatory measures to regulate social media use by the Chinese patent medicine (CPM) companies, it needs better understanding of CPM companies’ promotional activities using social media. Thus, this study aimed to analyze the nature of the information conveyed to the public by the CPM companies through microblog (Weibo) in China. Methods: The content of 17 CPM Weibo accounts was analyzed. These accounts were established by 13 CPM companies, each of which had more than 10,000 followers, over 1,000 posts and updated posts in 2016. Results: Of the 40,798 original posts identified in the 17 Weibo accounts, 98.39% (n=40,142) were classified into six main themes: (1) social living (36%); (2) health science (26%); (3) health maintenance (14%); (4) direct product promotion (11%); (5) corporate branding (7%); and (6) medical & industrial information (6%). Among the posts directly related to product promotion, more than half (n=2550) focused on customer interactions followed by product efficacy (n=945). Among the posts about corporate branding, about half of them (n=1,443) focused on company image. Conclusions: Weibo is being used by CPM companies widely for strategic product promotion. With one of the key strategies being overt marketing driven by covert marketing, a large amount of health-related information is disseminated through this platform. Regulatory policies to ensure the credibility of information disseminated in the social media used by the CPM companies for promotion purposes are warranted to help protect the public’s interests.