The present investigation was undertaken to assess anti-inflammatory and anti-arthritic efficacy and safety of T. chebula extract (TCE) in moderately osteoarthritic (OA) dogs. Dogs with OA received either 500 mg placebo or 500 mg TCE twice daily for 150 days. On a monthly basis, dogs were given a full physical exam and were evaluated for arthritic pain (overall pain, pain upon limb manipulation, and pain after physical exertion), inflammation (erythrocyte sedimentation rate, ESR), and analysis of complete blood count (CBC) and serum biomarkers of liver (bilirubin, ALT, and AST), kidney (BUN and creatinine), and heart and skeletal muscle (CK) functions. Elbow and stifle joints were radiographed on day 0 and day 150 for evaluation of arthritic progression. Dogs given TCE showed significant (P<0.01) reductions in overall pain, pain upon limb manipulation, and pain after physical exertion by day 90, with maximum effects on day 150 (81.2%, 81.5%, and 84.2%, respectively). A marked reduction in ESR coincided with pain reduction in TCE-treated dogs, which was indicative of anti-inflammatory effect of TCE. Radiographic evidence also indicated slowed progression of OA in joints examined. No significant change occurred in physical parameters, CBC parameters, or serum biomarkers in dogs on placebo or treatment, which suggested that TCE was well tolerated. It can be concluded that TCE, by having many active principles (chebulagic acid, chebulinic acid, corilagin, hydrolysable tannoids, etc.) might have provided antioxidant, anti-inflammatory and anti-arthritic effects in dogs without causing any side effects.