Purpose: The mechanism of improved endothelial function after statin treatment has been known as increased bioavailability of nitric oxide and it was independent of the cholesterol-lowering effects of statin therapy. The aim of this study was to evaluate the effect on endothelial function of statin according to dose. Methods: We enrolled the 60 patients with moderate cholesterolemia (total cholesterol 200~240 mg/dL). The patients were randomly divided as two groups according to dose of atorvastatin (10mg:30 patients, 40mg:30 patients). We measured the flow-mediated vasodilatation (FMD), aortic pulse wave velocity (PWV), intima-media thickness (IMT) of both common carotid artery, lipid profile and serum C-reactive protein at baseline, 1week and 8 weeks after medication of statin. Results: The total cholesterol and LDL level in both groups was significantly decreased 1 week and 8 weeks later. However, there is difference between groups only 8 weeks later. FMD of both groups was significantly increased in 1 week and 8 weeks, but not different between groups. PWV of only 40mg group was decreased both in 1week and 8 weeks, and in 8 weeks, different between both groups. However, the change of PWV was not correlated to the change of total cholesterol and LDL. Conclusions: The statin might be more effective in improvement of endothelial function as higher dose and longer duration of medication. Such the effect of statin on endothelial function may be independent to lipid lowering effect.