Introduction: Low back pain affects about 60% to 90% of the working-age population in modern industrial society. Myofascial pain syndrome is a condition characterized by muscles shortening with increased tone and associated with trigger points that aggravated with activity of daily living. Aim of work: To examine the effects of magnetic field therapy in patients with lower back myofascial pain syndrome. Materials and Methods: Thirty patients were assigned randomly into 2 groups. Subjects in the experimental group (n=15)with main age of 36.73(±2.52) received traditional physical therapy program (infrared radiation, ultrasonic, stretching and strengthening exercises for back muscles) as well as magnetic field , and control group (n = 15) with main age of 37.27(±2.52) received traditional physical therapy only. The following parameters including pain severity, functional disability and lumbar range of motion (flexion, extension, right side bending and left side bending) were measured before and after 4 weeks of treatment. Results: The results showed significant improvement in all parameters in experimental group compared with those of control group. Conclusion: On the basis of the present date, it is possible to conclude that a magnetic field is effective as a method of treatment for lower back myofascial pain syndrome patients with the parameters used in the present study.