Although concurrent associations among dispositional mindfulness, rumination, and depression have been identified, lacking is a study that longitudinally examines the relationships among these three constructs in a non-clinical sample of adults. We specifically sought to determine whether rumination mediates the expected negative association between mindfulness and depressive symptoms across time. A community sample of 483 adults completed self-report measures of mindfulness, rumination, and depressive symptoms initially and after 3 months and after 6 months. The predicted cross-lag associations were found, i.e. mindfulness predicted diminished rumination, and rumination positively predicted depressive symptoms, and as a consequence, the predicted longitudinal mediation was supported in the data as well. At the facet level of mindfulness, three of the five facets (i.e. acting with awareness, non-judging, and non-reacting) exhibited the longitudinal mediation through rumination to depressive symptoms. The findings of this research suggest that certain aspects of mindfulness function to reduce rumination, which then predicts diminished depressive symptoms.