The nefrotoxicity of prednisone in cats was evaluated, using an immunesupressor dose (5 mg/kg/day), by establishing blood count, serum biochemistry (urea and creatinine) and urinary (GGT, protein and creatinine) parameters and urinalysis. Eight cats were used. The animals were of undefinied breed, adults and with average weight of 3 kg. They were housed in four cubicles and fed with two measures of commercial ration per day and water ad libitum during an adaptation period of seven days. The trial design was entirely random, being rejected any specific criterion of inclusion in this study besides the absence of any previous kidney damage. Animals received 5 mg / kg prednisone, orally, every 24 hours for a period of 14 days. The samples were collected in two different times, with the animals resting before prednisone administration (M1), and 14 days after the administration (M2). Significant differences were found in some hematological and biochemical parameters as well as in urinalysis. It was concluded that the prednisone (5 mg / kg / day), during a period of 14 days, is potentially nephrotoxic and the determination of the urinary GGT activity was proven to be precisely sensitive to early proximal tubular injury.