OBJECTIVE： To study the antihypertensive effects of water decoction of Eupatorium lindleyanum on spontaneously hypertensive rats （SHR） and corresponding mechanism. METHODS： 50 SHR were randomly divided into model group， captopril tablets group （positive drug， 10 mg/g） and the groups of high， medium and low-dose （65.45， 32.73， 16.36 g/kg） water decoction of E. lindleyanum， with 10 rats in each group. The rats in the model group were given normal saline ig， while those in other groups were given corresponding drugs ig， once a day， for 7 consecutive weeks. The systolic blood pressure （SBP） and diastolic blood pressure （DBP） of the caudal arteries of the rats were measured every week， and the dynamic changes in the blood pressure of the rats as a result of drug intervention were recorded. The rats were sacrificed 7 weeks later， and the levels of endothelin （ET）， angiotensin （AngⅡ） and nitric oxide （NO） in serum were determined. RESULTS： After 7 weeks of drug use， compared to the model group， the rats in the drug administration groups had significantly lower SBP and DBP of the caudal artery （P＜0.05）， showing obvious dose-effect and time-effect relationships in the antihypertensive effect of water decoction of E. lindleyanum， and had obviously lower levels of NO and AngⅡ and markedly higher level of ET in serum， demonstrating a dose-effect relationship. CONCLUSIONS： The water decoction of E. lindleyanum has an obvious antihypertensive effect by a mechanism which may be related to decrease in the levels of NO and AngⅡ in serum and increase in the level of ET therein.