Background: knee osteoarthritis is one of the most common causes of chronic disability in the elderly. Despite the widespread application of low energy laser for pain treatment there is much controversy about its efficacy. The aim of this study was to investigate the analgesic effects of low energy laser in patients with knee osteoarthritis along with drug therapy and non - drug therapy in Tabriz within 2003. Materials and Methods: This clinical trial was carried out on 143 patients in two groups, the control (79 people) and the treatment (64 people). The treatment group received drug therapy, physical therapy and low energy laser for ten sessions, (with the intensity of 1 joule and the extent of 9 joule/cm2 in each knee) while the control group received only drug therapy and physical therapy. Pain intensity pre and post-treatment was graded by visual analog scale and compared using paired-t-test and independent-t-test. Results: Mean reduction of pain was 2.45±1.48 and 2.62±1.32 in control and treatment groups respectively. There was no significant difference between the control and treatment groups. Conclusion: According to the results of this study low energy laser was not more effective than routine drug therapy and physical therapy in patients with knee osteoarthritis. More experimental studies using laser intensity within different times are recommended.