Aim To evaluate the efficacy of amlodipin and enalapril on 24 h ambulatory blood pressure(ABPM) in elderly patients with mild to moderate isolated dystolie hypertension(ISH). Methods Sixty elderly patients whose average age was 64 years old with ISH were randomly divided into two groups and were treated with 5mg/d amlodipine,10mg/d enalapril respectively for 4weeks.The changes of ABPM were compared before and four weeks after treatment. Results (1)After 4 weeks treatment,there were significant differences in lowering systolic blood pressure(SBP), and pulse pressure(PP)in the two groups respectively. The total average systolic and diastolic blood pressure decreased by 17.03±8.55 mm Hg(p<0.001) and 4.83±4.82 mm Hg in the amlodipine group,by 14.30±7.26 mm Hg(p<0.001)and 4.97±2.87 in the enalapril group. 24 h mean blood pressure(MAP) decreased 8.86±4.76 mm Hg(p<0.001) in amlodipine group,decreased 8.74±3.07 mm Hg(p<0.001) in enalapril group.(2)PP was decreased by 16.97±14.06 mm Hg (p<0.001) in the amlodipine group,by 8.33±7.84 mm Hg(p<0.001) in the enalapril group.(3)Both drugs were similarly effective in 76.7% patients and 73.3% patient respectively (P=0.766),and goal blood pressure was achieved in 66.7% patients treated with amlodipin, 56.7% with enalapril (P=0.426).(4)The incidence of drug-related dependent side-effects were 6.67% in the amlodipine group,16.67% in the enalapril group. Conclusion (1)The data show that both amlodipin and enalapril can significantly decrease SBP, MAP and PP. There are no significant difference in lowering blood pressure between two groups.(2)Amlodipin 5mg,and enalapil 10mg once daily is effective and safe in patients with mild to moderate hypertension.