This study was aimed to investigate the antihypertensive effect of a polysaccharide fraction from Cordyceps sinensis on spontaneously hypertensive rats (SHR). The CSP1, one component of Cordyceps sinensis polysaccharides (CSP), was obtained after water extraction, deproteinization, de-colorization and purification with DEAE-cellulose 52. And a more homogeneous component CSP1-2 was obtained using Sepharose CL-6B chromatography. CSP1-2 mainly consisted of mannose, glucose and galactose in a molar ratio of about 2:2:1 and its average molecular weight was approximately 2.70×10(4)Da. Pharmacological tests showed that CSP1, in which the CSP1-2 was its main component, had antihypertensive effect by stimulating the secretion of vasodilator NO, decreasing the level of ET-1, epinephrine, noradrenaline and angiotensin II, inhibiting the increase of transforming growth factor β1 (TGF-β1) and lowering the level of inflammatory mediator of C-reactive protein (CRP). These results suggested that CSP1 may possess high potential in treating hypertension.