Drawing from dispositional mindfulness research and stress and coping theories, we tested whether adolescents’ dispositional mindfulness was associated with perceptions of peer victimization and exclusion and internalizing symptoms. We further explored the role of dispositional mindfulness as a protective factor buffering the impact of peer victimization and exclusion (PVE) on internalizing symptoms. Participants were 361 (40% boys) adolescents aged between 11 and 18 years (M = 14.9, SD = 1.4) who completed a questionnaire to assess dispositional mindfulness, perceptions of PVE, social anxiety and depressive symptoms, and loneliness. As expected, more frequent experience of PVE was associated with reporting more symptoms of social anxiety, depression, and loneliness. Further, adolescents who reported higher dispositional mindfulness also reported fewer symptoms of social anxiety, depression, and loneliness, even after controlling for gender and experiences of PVE. Dispositional mindfulness was not protective against (i.e., did not buffer) the effects of PVE on internalizing symptoms. Instead, we found that PVE had a stronger association with symptoms of social anxiety, depression, and loneliness when mindfulness was high relative to when it was medium or low. Yet, victimization was associated with greater social anxiety, depressive symptoms, and loneliness at all levels of mindfulness.