Abstract Objectives This study aims to investigate the impact of Mindfulness‐Based Cognitive Therapy (MBCT) for bipolar disorders on emotional responses by using skin conductance recording, and to investigate a mediating or predictive effect of cognitive reactivity. Methods Sixty‐seven patients with bipolar disorder were assessed at baseline, pre‐MBCT and post‐MBCT. After answering inventories regarding depression and dysfunctional attitudes, they were instructed to focus on emotional pictures from the International Affective Pictures System while electrodermal recording. Results For a subgroup of patients having a significant change of the electrodermal response, MBCT reduced dysfunctional attitudes and the amplitude of the physiological response to negative stimuli. Findings also show that lower dysfunctional attitudes at baseline predicted a larger reduction of physiological reactivity. Conclusions MBCT could decrease patient's reactivity to negative stimuli by decreasing its physiological component, which is coherent with its aim to facilitate disengaging from affective stimuli. Further studies are needed to better understand the mechanisms involved and how this could translate in reducing the risk of relapse.