Diabetes control as a chronic and complex disease needs doing self-care activity for lifetime. Psychological treatments, like acceptance and commitment therapy, are complementary to medical treatment in efforts to improve self-care activities. The purpose of present study was to investigate the effectiveness of acceptance and commitment group therapy on improvement of glycated hemoglobin and self-care activities in patients with type II diabetes. This was a pretest-posttest experimental design with control group. The study sample consisted of 100 (60 females, 40 males) out-patients diagnosed with type 2 diabetes who attended Labbafinejad Hospital. Measures used included: A questionnaire to obtain demographic and anthropomorphic characteristics and the Summary of Diabetes Self-Care Activities (SDSCA). The results yielded evidence for the effectiveness of acceptance and commitment therapy on improvement glycated hemoglobin levels and self-care activities. Follow-up comparisons after three months indicated that the beneficial effects of the intervention was still present. Based on the present findings, acceptance and commitment group therapy lead to the decrease of glycated hemoglobin and increase of self-care activities in type II diabetes. These findings suggest that acceptance and commitment therapy can be used as a complementary intervention together with medical treatment for improvement control indices of type II diabetes in order to prevent serious side effects of this illness.