Objective It is well documented that stress is associated with negative health outcomes in cancer patients. The purpose of this study was to assess the effects of a novel mindfulness intervention called mindfulness‐based art therapy (MBAT) versus standard educational support, on indices of stress and quality of life in breast cancer patients with high stress levels. Methods A total of 191 women were enrolled, stratified by age and stress level, and randomized to receive either an 8‐week MBAT intervention or a breast cancer educational support program of equal time and duration. Psychosocial stress was measured using the Symptoms Checklist‐90‐Revised, and quality of life was measured using the Medical Outcomes Study Short‐Form Health Survey at baseline, immediately post‐intervention, and at 6 months. Results Results showed overall significant improvements in psychosocial stress and quality of life in both the MBAT and educational support groups immediately post‐intervention; however, participants with high stress levels at baseline had significantly improved overall outcomes only in the MBAT group, both immediately post‐intervention and at 6 months. In addition, at 6 months follow‐up, participants attending five or more sessions trended toward retaining treatment effects better in the MBAT than in the control group. Finally, black women and white women were similar in terms of how they benefited from the MBAT intervention, even though white participants tended to have higher educational level and marital status. Conclusions In conclusion, MBAT is associated with significant, sustained benefits across a diverse range of breast cancer patients, particularly those with high stress levels. Copyright © 2013 John Wiley & Sons, Ltd.