This retrospective study investigated the impact of amino acid supplementation on body weight, serum albumin, creatinine and urea concentrations, and urine protein-to-creatinine (UPC) ratio in proteinuric dogs with chronic kidney disease (CKD). Forty-six client-owned azotemic dogs with spontaneous proteinuric CKD already on a renal diet and in therapy with enalapril were included. After approximately 1 month of treatment (baseline), 29 dogs received oral amino acid supplementation daily (group A) and 17 dogs did not (group B). The parameters under investigation were determined at baseline and after 4 to 8 weeks in both groups. Compared to baseline, body weight and serum albumin increased (P < 0.01, P < 0.05, respectively) at follow-up in group A, but did not change in group B. Serum creatinine concentration did not change in both groups; urea concentration (P < 0.05) and UPC ratio (P < 0.01) decreased in group B, but not in group A. Supplementation with amino acids increased body weight and serum albumin concentration in these dogs but it might have prevented a decrease in proteinuria and urea concentration.