The excessive use of social media is prevalent among undergraduates. Dark triad personality is one of the significant predictors of social media addiction, but inconsistent findings were reported. This study adopted the personality-coping-outcome theory as a framework to examine whether coping strategies mediate the effects of dark triad personality on social media addiction. The purposive sampling method was used to recruit 219 undergraduates for a survey. The results showed that only narcissism is associated with social media addiction, and only avoidance coping strategy mediated the effects of pathology on social media addiction. It is suggested a complete theory is required to explain the relationships between dark triad personality and social media addiction, and a coping scale to be developed to cover the coping strategies that fit dark triad personality.