Background Aliskiren is a novel blood pressure-lowering agent acting as an oral direct renin inhibitor.The aim of this study was to assess the effect of aliskiren on arterial stiffness,compared with that of ramipril in mild to moderate essential hypertensive patients.Methods Following a two week placebo run-in period,patients with a mean sitting diastolic blood pressure (ms-DBP) ＞95 and ＜110 mmHg (1 mmHg=0.133 kPa),and a mean sitting systolic blood pressure (ms-SBP) ＜180 mmHg were randomly allocated to treatment with aliskiren (150 mg/d,n=20) or ramipril (5 mg/d,n=20) for eight weeks.Blood pressure,plasma renin activity,and the brachial-ankle pulse wave velocity (ba-PWV) were measured before and after eight weeks of treatment.Results Eight weeks of treatment significantly decreased systolic blood pressure and diastolic blood pressure in both the aliskiren group and ramipril group.The hypotensive effect did not differ between the two groups.Plasma renin activity decreased after aliskiren treatment and increased after ramipril treatment.There was no significant difference in baseline ba-PWV between the aliskiren and ramipril groups (P=-0.892).The ba-PWV was significantly reduced in both the aliskiren group (1535 (1405-1666) vs.1464 (1360-1506) cm/s) (P ＜0.01) and the ramipril group (1544 (1433-1673) vs.1447 (1327-1549) cm/s) (P ＜0.01).No statistically significant difference was found in the decline of ba-PWV between the two groups (P=0.766).Conclusions The current study revealed that aliskiren (150 mg/d) could ameliorate arterial stiffness and its effect was similar to ramipril (5 mg/d) in mild to moderate hypertensive patients,indicating that in addition to lowering blood pressure,aliskiren had beneficial effect on vascular protection.