Objectives To study the changes of nitric oxide, angiotensin Ⅱ and superoxide anion in renal artery hypertension pathogenesis. Methods Male Wistar rats weighing 256 -285g were divided into 5 groups randomly, 10 rats of each group. Control group:false operation was made and routine diet was given; Ligature group: left renal artery was ligatured uncompletely and routine diet was given; Ligature + Losartan group:left renal artery was ligatured uncompletely and Losartan ture + L -Arg group: left renal artery was ligatured undrinking water; Ligature + L - Arg + Losartan group: left the drinking water. Blood pressure and heart rate were measured before and at the end of the experiment. One week after ligature, blood was drawn to determine angiotensin Ⅱ, cGMP, nitric oxide, nitric oxide synthase (NOS), O2-, superoxide dismutase (SOD). Results Systolic blood pressure was higher in ligature group than that in control group (p＜0.05), systolic blood pressure was much lower in ligature + Losartan group than that in ligature group. Heart rate did not change significantly after experiment (p ＞ 0. 05 ). AngⅡ was higher in ligature group than that in control group, even much higher in ligature + Losartan group (p ＜ 0. 01 ). There was no difference of cGMP in each group (p ＞ 0. 05 ). The concentration of NO was lower in ligature group (p ＜ 0. 05 ), NO was higher in ligature + L - Arg + Losartan group than that in ligature group (p ＜ 0. 05). O2’ was higher in ligature group and ligature + L - Arg group than that in control group (p ＜ 0. 05), O2- was lower in ligature + Losartan group than that in ligature group (p ＜0. 05). The level of SOD was lower in ligature group than that in control group (p ＜ 0.05), higher in ligature + L - Arg group and ligature + L - Arg + Losartan group than that in ligature group (p ＜0.05). Conclusions AnglⅡ,O2- and NO imbalance play an important role in hypertension pathogenesis, L-Arg and losartan may have protective effect.