PurposeThis study aims to investigate the antecedents and outcomes of excessive use of personal social media at work. The prevalence of personal social media in the work environment can easily lead to excessive use and negative consequences. Understanding the predictive factors and negative consequences of employees' excessive use of personal social media at work is important to develop their appropriate use of social media and improve their job performance.Design/methodology/approachBased on dual-system theory and the person-environment fit model, this study develops a research model to examine the effect of habit and self-regulation on excessive use of personal social media at work and that of the outcomes of excessive use on employee job performance through strain. This study conducts a questionnaire survey on 408 employees to test the research model and hypotheses empirically.FindingsResults suggest that the imbalance between habit and self-regulation drives excessive personal social media use of employees at work. Furthermore, excessive use of personal social media has a strong impact on employee strain, which can significantly decrease job performance.Originality/valueFirst, this study considers excessive use of personal social media at work as a result of two different cognitive systems, that is, an automatic system and a controlled system, thereby extending the dual-system theory to explain excessive use of personal social media in the work context. Second, unlike previous studies that focused on the outcomes or explored the antecedents of excessive social media use at work respectively, the study employs the person-environment fit model and examines the systematic influence of excessive social media use at work from a broad perspective by linking its antecedents and outcomes.