Derris Scandens Benth (family : Leguminosae) is a woody vine growing throughout Southeast Asia, including Thailand. The stem of D.Scandens has been widely use in Thai traditional medicine, foe example of myalgia. Previous study shown that D.Scandens Benth extract has the anti-inflammatory activity. Although NSAIDs are efficaciously in the treatment of osteoarthritis,but the GI side effect is still concerned. In this study we aim to investigate the efficacy and safety of D. Scandens Benth extract compared with Naproxen for therapy of patients with knee osteoarthritis.