Objectives : The aim of this study was to investigate the effectiveness of group cognitive-behavior therapy on decreasing severity of pain and psychological distress among women with chronic back pain. Method: This research is a semi-experimental study with pretest-posttest design and control group. Among females with chronic back pain referred to Imam Khomeini Hospital and a clinic in Tehran in 2010, 30 participants with mean age of 33 years and 7 months were selected and randomly assigned to two equal experimental and control groups. Experimental group during twelve 90-min sessions received Turk and Free cognitive-behavior therapy, and control group were just followed. All participants completed the items of Depression, Anxiety, and Stress Scale (DASS), and Quebec Back Pain Disability Scale (QBPDS) prior to and after the intervention. The data were analyzed using independent t-test. Results: The findings revealed a significant decrease of back pain (p<0.05), and depression, anxiety and stress symptoms (p<0.05) in experimental group who participated in therapeutic sessions. Conclusion: Cognitive-behavior therapy could minimize adverse effects of pain and decrease psychological distress by changing dysfunctional behaviors, correcting counterproductive cognitions and deteriorating sensations related to pain.