Mindfulness is known to decrease anger and aggression. Self-compassion is a related and relatively new construct that may predict other clinical outcomes more strongly than does mindfulness. Little research has focused on whether self-compassion is related to anger and aggression, and no studies have explored mechanisms of these associations. The current survey study explores whether angry rumination mediates the unique associations between self-compassion and anger and aggression, controlling for trait mindfulness. Two hundred and one undergraduates completed questionnaires assessing self-compassion, mindfulness, angry rumination, and recent anger and aggression. Supporting our hypotheses, angry rumination mediated the associations between self-compassion—particularly its over-identification subscale—and anger and aggression when controlling for mindfulness. Mindfulness did not predict angry rumination, recent anger, or aggression when controlling for self-compassion. Furthermore, multiple regression analyses predicting aggression-related variables indicated that angry rumination uniquely predicted over-identification, one of the six self-compassion subscales. These findings suggest that self-compassion, particularly a lack of cognitive and emotion fusion, may be a more proximal predictor of clinical outcomes than mindfulness. Implications for current conceptualizations and measures of mindfulness are discussed. Self-compassion may be useful for developing clinical interventions targeting anger and aggressive behavior.