Abstract: Objective To study the effect of the angiotensin receptor blocker（ARB）on the salt sensitivity of blood pressure in Dahl salt-sensitive（Dahl S）rats. Methods Experiment 1,the mean arterial blood pressure（MAP）of Dahl S rats was monitored by radio telemetry and,after baseline measurements,the rats were treated with either vehicle（n=8）or the ARB olmesartan100nmol/（kg·h）,subcutaneously（n=7）. The rats were fed the 0.5%salt diet during the baseline period and the first 7dof treatment,the diet was then switched to one containing 8%salt for another 7d,and the rats were returned to the 0.5%salt diet for the final 7d. Salt sensitivity was indicated by the slope of the Na-MAP relationship. Experiment 2,Dahl S rats were divided into 4groups:normal diet（0.5%salt;NS）,8% high salt diet（HS）,and NS or HS plus olmesartan groups. On day 7after the end of the experiment,renalrenal cortical nicotinamide adenine dinucleotide phosphate NAD（P）Hoxidase activity and p22phox mRNA levels and urinary（24hurine H2O2 excretion）oxidative stress levels were measured. Results In the first experiment,the MAPs in control group which were measured at baseline,7days’ after 0.5%salt diet,7days’ after 8%salt diet and 7days’ after returned 0.5% salt diet were（124.0±2.0）,（138.6±2.7）,（120.7±2.5）mm Hg respectively while those in ARB group were（99.1±1.6）,（127.2±3.6）,（92.5±2.0）mm Hg. The slope of the Na-MAP relationship showed no significant difference between control group and ARB group（P＞0.05）. In the second experiment,systolic blood pressure（SBP）,renal cortical NAD（P）H oxidase activity,renal cortical p22phox mRNA levels,24hurine H2O2excretion（149.3±7.9）vs（120.8±5.1）mm Hg,（347.7±23.6）vs（253.2±11.8）CPM×103/mg pro,0.70±0.08vs 0.53±0.07,（151.0±17.9）vs（40.2±6.3）nmol/（L·24h）,all P＜0.01were significantly increased,and plasma angiotensin Ⅱ concentration（26.4±4.0）vs（49.8±4.1）pmol/L,P＜0.01was significantly reduced in the HS group compared with the NS group.SBP,renal cortical NAD（P）H oxidase activity,renal cortical p22phox mRNA levels,24 h urine H2O2 excretion,renal cortical angiotensinⅡconcentration（113.7±6.4）vs（149.3±7.9）mm Hg,（277.1±19.0）vs（347.7±23.6）CPM×103/mg pro,（0.54±0.08）vs（0.70±0.08）,（108.4±11.2）vs（151.0±17.9）nmol/（L·24h）,（73.1±7.0）vs（162.1±15.4）fmol/g tissue,all P＜0.05)were significantly reduced,and plasma angiotensin Ⅱ concentration（61.3±5.7）vs（26.4±4.0）pmol/L,P＜0.05was significantly increased in the HS plus ARB group compared with the HS group. Conclusion We have demonstrated that ARB olmesartan can significantly reduce blood pressure,even for the high salt diet,and does not affect salt sensitivity in Dahl S rats.The effects of it could be in part due to renal cortical oxidative stress levels.