This study was designed to evaluate the clinical efficacy and safety of Rhubarb extracts ($Rubenal^{(R)}$) in dogs with chronic renal failure (CRF). Client-owned 40 dogs with CRF graded International renal interest Society (IRIS) II-III were enrolled in this study. The dogs were equally allocated and blindly administered with $Rubenal^{(R)}$ or placebo. The following items were evaluated at day 0, 30, 90 and 180: body condition score (BCS), clinical score (appetite, polydipsia/polyuria, quality of life score), hemogram (WBC, RBC, PCV), serum biochemistry (ALT/AST, ALP, Creatinine/BUN, total protein, albumin), serum electrolyte (Na, K, Cl, Ca, P), systolic blood pressure, urinalysis (UPC, USG) and IRIS stage. In this study, we found that the $Rubenal^{(R)}$ preparation was well tolerated by dogs and induced no adverse effects. Statistically significant improvements were observed in clinical score (quality of life score by vet and clients), serum BUN and creatinine levels, serum phosphorus concentration, level of proteinuria, and the IRIS score of CRF in dogs after 6 month of treatment of $Rubenal^{(R)}$. Those findings suggested that the Rhubarb extracts can improve the clinical signs of CRF (i.e. azotemia, hypertension, proteinuria, hyperphosphoremia) and the quality of life (i.e. BCS, clinical score) and can retard the progression of CRF in dogs. Therefore the Rhubarb extracts can be a good supplementary drug for treating dogs with subclinical and clinical renal diseases. However, care should be taken for interpreting our result, because this study is not double-blinded controlled study but pilot study.