With people������������������s heavy use of mobile phones, social media on mobile devices successfully get users to adopt their different features for the various gratifications and provide corporations an interactive and effective platform to engage their publics for corporate social responsibility (CSR) activities and relationship management. However, in current literature of public relations, little research ever focused on mobile communication or analyzed media stakeholders and publics on mobile devices (Vercic, Vercic, & Sriramesh, 2015). This study aims to address the gap in mobile communication and public relations areas by integrating uses and gratification theory and organization-public relationship (OPR) theory and examining the relationships among mobile corporate social responsibility (mCSR) activities, gratifications, social media engagement, and the organization-public relationship. By employing a mixed research method in collecting data from both United States (U.S.) and China, this research not only conducts survey research of 1,500 participants, but also generates in-depth information about how mCSR can best be practiced in the online environments of two nations. The U.S. and China were selected for two main reasons. First, they represent the largest markets in, respectively, North America and the Asia-Pacific region (Hung-Baesecke, Chen, & Boyd, 2016). Second, these two largest markets worldwide are different from each other in the local market conditions such as economic, social, cultural, media, and political contexts, and the relationship among the central government, corporations, and publics (Bortree, 2014; Hung-Baesecke, et al., 2016). Findings will present the role of mobile-based communication in engaging the publics on CSR activities. This comparative study will also illustrate the impact of contextual factors on mCSR engagement and relationship outcomes. Theoretical and practical implications of this study are discussed.