Objective To investigate the relationship between angiotensin Ⅱ ( AngⅡ) and transformation of vascular fibroblasts phenotype .Methods Eighteen rats were randomly assigned into the untreated group , mini-pump infusion of saline group and mini-pump infusion of AngⅡgroup which was used as the hypertension model .Their systolic pressure and vascular morphology were examined .The expression of catalase ( CAT ) and 4HNE was examined by immunohistochemistry .Western blotting was used to examine the expression of CAT of adventitial fibroblasts which were cultured by different incubation times and concentrations of Ang Ⅱ.Results Compared with untreated and mini-pump infusion of saline groups , the systolic pressure and carotid media thickness stained by HE of mini-pump infusion of AngⅡgroup were significantly higher (P<0.01).The results of immunohistochemistry showed that the expression of CAT ofAngⅡgroup was significantly lower than that of untreated group , however the expression of 4HNE of AngⅡgroupwas higher than that of untreated group (P<0.05).Furthermore, the results of Western blotting indicated that the effect of Ang Ⅱ on down-regulation of CAT function was in a dose and incubation time dependent manner .Conclusion AngⅡdown-regulates adventitial CAT expression and promotes fibroblasts phenotypic transformation which leads to pathological arterial vascular remodeling .