BACKGROUND: With the increasing incidence of mobile phone addiction, mobile phone addiction has been considered to be related to adolescents' psychological distress. However, the underlying mechanisms of this relation were still unclear. The present study tested the mediating role of rumination and the moderating role of the capacity to be alone in the relation between mobile phone addiction and psychological distress. METHODS: 754 middle school students were recruited to complete measures of mobile phone addiction, rumination, the capacity to be alone, psychological distress and demographic variables. RESULTS: Mobile phone addiction was significantly and positively associated with psychological distress, and this link could be mediated by rumination. Moreover, the direct effect of mobile phone addiction on psychological distress and the indirect effect of rumination in this link were moderated by the capacity to be alone. Both these two effects were stronger for adolescents with lower capacity to be alone. LIMITATIONS: The present study is limited in terms of its sample selection, cross-sectional design, and self-reported instruments. CONCLUSIONS: The present study advances our understanding of how and when or for whom mobile phone addiction is related to serious psychological distress. Education professionals and parents should pay special attention to the psychological distress of adolescents suffering from mobile phone addiction, particularly for those with lower capacity to be alone.