This paper reports on a study designed to explore the educational affordances of mobile social media and how teachers' private theories mediate integration of the affordances in teaching practice in higher education in China. Four university teachers were included as cases for an in-depth inquiry in this study. Qualitative data were collected through multiple methods, including observations, interviews and documents such as written reflections provided by the participants. Thematic content analysis was performed to explicate categories of affordances and private theories. Nine categories of affordances of mobile social media emerged from the results. Analysis of data also exposed a number of areas of private theories that influenced the decisions for technology integration of different teachers. Theories about Learning most productively mediated instructional decisions leading to student-centered practices while other theories were leading to more traditional practices. Private theories of the participants transformed with their adoption of affordances of mobile social media, and thus reflection emerged as a critical strategy for productively transforming teachers' private theories. Moreover, recommendations for practitioners are delivered and suggestions for future research are provided.