Mindfulness-Based Cognitive Therapy(MBCT) is a promising intervention to prevent depressive relapse. Yet beyond efficacy studies, little is known regarding the mechanisms that could be modified through MBCT. Objectives of the present study were twofold: determine whether cognitive functioning was altered among patients remitted from depression at admission in a MBCT trial; and document possible changes during the trial and follow-up. In a cross-sectional perspective, cognitive functioning (autobiographical memory, shifting capacities, dysfunctional attitudes, mindful attention awareness and rumination habits) was first compared between 36 patients remitted from depression, 20 acutely depressed patients and 20 control participants. In a longitudinal perspective, changes in the remitted sample were explored during a MBCT plus Treatment As Usual versus Treatment As Usual randomized controlled trial and 9-month follow-up. Performances of remitted patients were similar to the ones of control participants for autobiographical memories, shifting capacities, and mindful attention awareness, whereas levels of rumination and dysfunctional attitudes were significantly elevated. Participation in the MBCT program was accompanied with a significant decrease of dysfunctional attitudes that continued up to 9-month postintervention. No other change was observed that was specific to MBCT. Results suggest that MBCT might help people to identify dysfunctional attitudes at a very early stage and to avoid engaging further in these attitudes.