Exercise training (Ex) slows the progression of hypertension and renal failure in some animal models. We and other groups have reported that Ex ameliorated hypertension and renal dysfunction in spontaneously hypertensive rats. Since little has been reported on the effects of Ex on renal disorder in salt-sensitive hypertension, we investigated the effects of Ex on blood pressure and renal function in Dahl salt-sensitive (DS) rats. Six-week-old male DS rats were divided into three groups: 1) Normal salt (0.5% NaCl) diet (NS) (NS group, n=10), 2) High salt (8% NaCl) diet (HS) (HS group, n=11), 3) HS plus moderate Ex with treadmill running (HE group, n=11). After 8 weeks, HS induced severe hypertension, and Ex did not affect systolic blood pressure (114±3, 209±6 and 205±8 mmHg in the NS, HS and HE groups, respectively). Plasma creatinine was significantly higher in the HS and HE groups than in the NS group, but not different between the HS and HE groups (0.22±0.01, 0.44±0.03 and 0.40±0.03 mg/dl). Urinary protein and albumin significantly increased in the HS and HE groups, but these were significantly lower in the HE group compared with the HS group (Protein: 15.9±1.6, 432.8±36.8 and 327.2±22.3 mg/day. Albumin: 3.9±0.8, 195.2±15.2 and 154.2±11.1mg/day). Urinary TBARS, an index of oxidative stress, significantly increased in the HS and HE groups, but this was significantly lower in the HE group compared with the HS group (0.30±0.02, 0.75±0.06 and 0.53±0.03 mg/day); there was no significant difference in plasma TBARS among all groups. CYP4A1 and CYP4A2 protein expressions in the outer medulla were significantly lowered by 37% and 48% in the HS group compared with the NS group, and were significantly elevated by 40% and 150% in the HE group compared with the HS group. There was no significant difference in cortical CYP4A1 protein expression among all groups. Although there was no difference in cortical CYP4A2 between the NS and HS groups, it was significantly increased by 35% in the HE group compared with the HS group. These results suggest that Ex attenuated HS-induced proteinuria independently of blood pressure or plasma creatinine level in DS rats. The improvement of oxidative stress and CYP4A expression in the kidneys may contribute to the renoprotective effects of Ex in DS rats.