Abstract: OBJECTIVE To investigate the effect of losartan on Kallikrein expression in spontaneously hypertensive rats(SHR). METHODS Sixteen ♂ SHR rats were randomly divided into hypertension model group and losartan group, while eight ♂ normotensive Wistar-Kyoto rats was normal blood pressure group. Non-invasive blood pressure measuring instrument monitored systolic blood pressure(SBP) of each group rats in every week. The serum levels of total Kallikrein, NO and PGI₂ were measured. Aorta change was evaluated with histopathologic examination by HE staining. qRT-PCR tested the gene expression change of Kallikrein. And the expression of Kallikrein in aortic tissue was measured by Western blotting. RESULTS After 4 weeks of continuous administration in SHR rats, the SBP of the losartan group decreased in a time-dependent manner. The serum levels of Kallikrein, NO and PGI₂ in rats increased by 54.1%, 49.5%, and 49.2%, respectively. Histopathology showed that the vascular remodeling phenomenon in the losartan group was significantly lower than that in the model group. qRT-PCR showed that the expression of Kallikrein in the losartan group was up-regulated by 66.7%. Western blotting showed that Kallikrein protein expression and gene expression in the losartan group were consistent and positively correlated. CONCLUSION Losartan decreasing SBP and improving vascular remodeling from SHR rats may be related to up-regulation of Kallikrein expression.