Breast cancer has a higher incidence than any other type of malignant tumor among women in Taiwan. The psychological effects on these patients, in addition to the physiological treatment, warrant more attention. Research has indicated that art therapy provides people with holistic, comprehensive adjuvant therapy; these mutually supportive groups can even promote changes in the body, mind, and spirit of patients with cancer. This study aimed to enhance the mental health and quality of life of patients with postoperative breast cancer through group art therapy and verify the efficacy of group art therapy in achieving these outcomes. This study adopted a randomized controlled trial design and purposive sampling to recruit patients with postoperative breast cancer who met the eligibility requirements and who agreed to participate in the study. The sample was divided into intervention and control groups. The intervention time for group art therapy was 2 hours once per week for a total of 6 weeks. We collected data on participants' depression and anxiety as well as their quality of life before the first week of the intervention and at the end of the sixth week. Analysis of covariance was used to compare the intervention and control groups after members of the intervention period. A total of 36 participants were enrolled in the study; 20 were in the intervention group, and 17 were in the control group. In this study, group art therapy significantly ameliorated anxiety and enhanced quality of life among women who had received breast cancer operations (p = .016, .001), thus verifying its efficacy. More research on group art therapy should be conducted for acquiring empirical data that can be used to alleviate the psychological burden on patients with postoperative breast cancer.