Nonsteroidal anti-inflammatory Drugs (NSAIDs) is one of the most commonly use medication for treatment of knee osteoarthritis which has the analgesic and anti-inflammation by inhibition of prostaglandin synthesis via COX-1 and COX-2 isoenzyme. The problem of prolong using NSAIDs has side effect on kidney, liver and GI system. Curcumin longa extract Curcumin) is the Asian herbal medicine that has the anti-inflammatory effect by down regulate activation of NF-kappaB and proinflammatory cytokines such as Tumor Necrotic Factor-alpha, Interleukin-1, Interleukin-8, and Nitric Oxide Syntase. Many research data had advocate for the combination therapy which can increase safety and efficacy with less side effect compare with monotherapy regimen especially when the medicine has the different mechanism of action. The present study is the double blind prospective randomized control trial to evaluate the efficacy of curcumin as an adjuvant therapy of diclofenac in primary knee osteoarthritis. 44 patients were randomized to take NSAIDs (diclofenac) 75 mg/d with placebo and the other 44 took NSAIDs (diclofenac) 75 mg/d with curcumin 1,000 mg/d for 3 months. The authors evaluated the Visual Analog Scale (VAS) for pain and Knee Injury and Osteoarthritis Outcome Score (KOOS) every month for 3 months. At the end of study 36 patients were completed for the first group and 37 for the study group. There was no difference in VAS [p-value = 0.923 (F = 0.009)]. The KOOS was analyzed in 5 categories symptom, pain, function in daily living, function in sport and recreation and knee related quality of life. The curcumin with diclofenac group had tendency to be better in Pain and Function in daily living, but there were no statistic different in all group [p-value = 0.412 (F = 0.683), p-value = 0.814 (F = 0.056), p-value = 0.446 (F = 0.589), p-value = 0.224 (F = 1.511) and p-value = 0.938 (F = 0.006)]. In conclusion, the adjuvant therapy ofcurcumin with diclofenac has the potential beneficial effect in comparison with diclofenac alone, but no statistical significance.