This study explored teachers' classroom integration of mobile social media at universities in China and how their technology integration was influenced by institutional factors from the perspectives of Activity Theory. A qualitative multi-case study approach was adopted to address the research question. Data were collected from multiple sources, including classroom observation, semi-structured interviews, and documents provided by the participants. Qualitative content analysis was conducted to analyse the data. Results showed that different types of universities exerted different institutional influences on teachers' classroom technology integration in China, in terms of rules, community, and division of labour. The public university provided a more supportive environment for technology innovation than the private university did in this study. A framework for enhancing institutional impact on teachers' technology use is proposed and suggestions for future research are provided.