Objective: To compare the effects of spinal stabilization exercise against with lumbar extensor strengthening exercise. Method: Sixty patients with chronic low back pain were enrolled into the study and randomly classified into three groups. Groups were treated with spinal stabilization exercise (Group 1), lumbar extensor strengthening exercise using a MedX machine (Group 2), or with a combination program (Group 3) for 8 weeks. Patients were not given any other treatment modalities. Isometric peak torque of the lumbar extensors, pain rating score (PRS), Medical Outcomes Study Short Form-36 (SF-36) score, and the Oswestry low back pain disability questionnaire (OLBPD-Q) were assessed at 0, 4, and 8 weeks of exercise. Results: 1) After 8 weeks, all groups showed incremental improvements in maximal isometric torque of the lumbar extensors and exhibited improvement in SF-36, PRS, and OLBD-Q scores (p＜0.05). 2) There were no significant differences in the degree of improvement among the three groups after 8 weeks of exercise. 3) The percentage of patients with scores of good or excellent in Group 3 was higher than in Groups 1 and 2 according to all evaluation tools. Conclusion: In the treatment of chronic low back pain, all exercise groups showed decreased pain, improved quality of life, and increased lumbar extensor strength regardless of the exercise type employed. We suggest that exercise programs in general are effective for the treatment of chronic low back pain and a combination exercise program seems to be most beneficial. (J Korean Acad Rehab Med 2008; 32: 570-575)