Aim To investigate the effect of estrogen replacement therapy (ERT) on the myocardial and kidney fibrosis in spontaneously hypertensive rats (SHR). Methods SHR were randomly divided into 3 groups:sham operation; ovariectomy with estrogen replacement therapy; ovariectomy treated with placebo. The rats were given normal diet and were killed three months after the operation. Systolic blood pressure, body weight, left ventricular mass were measured. Transforming growth factor β 1 (TGF β 1) in the myocardium and kidney were analyzed by immunohistochemical techniques. Myocardial interstitial collagen was analyzed using picrosirius red technique and computer image analysis system. Results Estrogen plasma levels dropped in ovariectomized rats compared with sham operate rats and recovered after estrogen substitution; the systolic blood pressure (SBP) was significantly higher in ovariectomied rats than that in normal group, no obvious change was showed between ovariectomied rats after ERT and sham operate group; TGF β 1 expression was increased in the left ventricle and kidney of overiectomied rats, and significantly decreased after ERT compared with ovariectomied group; the left ventricle of heart to body weight ratio in ovariectomied rats was significantly higher than that in sham operate rats. The ratio was decreased after treatment with estrogen; the ovariectomied rats had a highter interstitial collagen volume fraction (CVF), ERT could significantly reduce CVF. Conclusions ERT could prevent the increasing of SBP and the kidney and myocardial fibrosis in ovariectomied rats.