Abstract: Objective: The goal of present study was to investigate the changes of vascular endothelial relaxation of spontaneously hypertensive rat (SHR)and the function of amlodipine to improve vascular endothelial dysfunction of SHR. Methods: The animals were divided into three groups:SHRs control group,amlodipine group and WKY group.Blood presure was messured by the tai-l cuff method.After been treated by amlodipine,Rats were studied to observe the endothelium-dependent relaxation of the rings of thoracic aorta to Ach. Results: In SHR,amlodipine can reduce the blood pressure significantly(27.5±2.7)kPa vs(18.5±2.2)kPa (P=0.0000).Endothelium-dependent relaxations of the rings from SHRs control group were significantly depressed as compared with those in WKY rats(P=0.0006).Compared with SHRs of control group,the maximal endothelium-dependent relaxation to Ach was enhanced markedly after treatment with amlodipine(78.8%±8.6%) vs (64.7%± 10.2%)(P=0.019),but still decreased as compared with those in WKY rats(78.8%±8.6%)vs (90.01%±11.4%) (P=0.0418). Conclusion: Our results indicate that the endothelium-dependent vascular relaxation is attenuated in SHR,Longterm antihypertensive therapy with Amlodipine reduced blood presure and improved endothelial relaxation in SHR.