As mobile social network has become an important component of people’s daily life, it poses a significant challenge on knowledge workers’ limited attention. However, studies on how mobile social network affects knowledge workers’ attention management are lagging. In this research-in-progress, we attempt to fill the research gap by developing a research model to understand the underlying mechanism. Based on the resource allocation theory, we propose that mobile social network engagement affects focused attention, and the effect varies upon the social network content. Extending the unconscious thought theory, we propose that focused attention affects task performance, and task types moderate this relationship. A laboratory experiment will be conducted to test the proposed hypotheses. This study has both theoretical and practical implications. Theoretically, this study is effective in understanding how mobile social network usage affects knowledge workers’ focused attention and task performance. Practically, this study sheds light upon how to manage the use of mobile social network in the workplace.