This study investigates the impact of different levels of dietary protein on dogs with a reduced renal mass. Thirty-one adult dogs of different breeds underwent unilateral nephrectomy and received a low protein diet (18%) (A) for 2 months. Then, 15 dogs were switched to a high protein diet (34%) (B) while the remaining 16 continued with the previous diet. Glomerular filtration rate (GFR) and urine protein to creatinine (UPC) ratio were determined at the beginning of the diet trial and every 6 months. After 48 months, 10/16 dogs of the Group A survived compared to 13/15 of the Group B. No differences in GFR were found among survivors.