Chronic renal failure (CRF) represents a world health problem. Ozone increases the endogenous antioxidant defense system, preserving the cell redox state. The aim of this study is to evaluate the effect of ozone/oxygen mixture in the renal function, morphology and biochemical parameters, in an experimental model of CRF (subtotal nephrectomy). Ozone/oxygen mixture was applied daily, by rectal insufflation (0.5 mg/kg) for 15 sessions after the nephrectomy. Renal function was evaluated, as well as different biochemical parameters, at the beginning and at the end of the study (10 weeks). Renal plasmatic flow (RPF), glomerular filtration rate (GFR), the urine excretion index, the sodium and potasium excretions (as a measured of tubular function) in the ozone group were similar to sham group. Nevertheless, nephrectomyzed rats without ozone (positive control group) showed the lowest RPF, GFR and urine excretion figures, as well as tubular function. Animals treated with ozone presented systolic arterial pressure (SAP) figures lower than the positive control group, but higher values with respect to sham group. Serum creatinine values and protein excretion in 24 hours in the ozone group were decreased comparing with nephrectomyzed rats, but still higher than normal values. Histological study demonstrated that animals treated with ozone presented less number of lesions in comparison with nephrectomyzed rats. Thiobarbituric acid reactive substances were significantly increased in nephrectomyzed and ozone-treated nephrectomyzed rats in comparison with sham group. In the positive control group, superoxide dismutase (SOD) and catalase (CAT) showed the lowest figures in comparison with the other groups. However, ozone/oxygen mixture induced a significant stimulation in the enzymatic activity of CAT, SOD and glutathione peroxidase, as well as reduced glutathione in relation with sham and positive control groups. In this animal model of CRF, ozone rectal administrations produced a delay in the advance of the disease, protecting the kidneys against vascular, hemorheological and oxidative mechanisms. This behavior suggests ozone therapy has a protective effect on renal tissue by down regulation of the oxidative stress present in CRF.