[Abstract] Objective To evaluate the efficacy and tolerability of the fixed combination of amlodipine 2.5 mg/telmisartan 40 mg once-daily therapy ,compared with amlodipine 5mg ,monotherapy in patients with mild and moderate hypertension, and to evaluate the 24 h antihypertensive efficacy and the duration of action by ambulatory blood pressure monitoring Methods In a randomized,double-blind ,parallel controlled teial,360 cases of hypertensive patients after 2 weeks wash-out,and then given 4 weeks of amlodipine 2.5 mg monotherapy,238 patients with mean seated diastolic blood pressue(SeDBP) remain ≥90 mmHg or/and systolic blood pressure (SeSBP) rained ≥140mmHg(1mmHg=0.133kPa) were randomly divided into telmisratan 40 mg/amlodipine 2.5 mg fixed-dose combination therapy group (once a day , n=113), and amlodipine monotherapy group (daily 5 mg , n=125).In the two groups the BDP≥90mmHg or/and SBP≥140mmHg were doubled the dosage of the initial regimen at the end of 8-week treatment for additional 8 weeks, and the patients with DBP＜90mmHg and SBP＜140mmHg remained the initial regimen. The primary endpoint was to evaluate the improvement of DBP and SBP at the end of 16-week treatment . There were 78 patients (the combination therapy group n=32,monotherapy group n=46) completed the 24 h ambulatory blood pressure monitoring which was in the final efficacy analysis . Results The randomized ,double-blind treatment for 16 weeks,the mean value of SeDBP and SeSBP reduction ,the reaching target blood pressure rate and total successful response rate to the treatment were (10.7±5.8)mmHg,(14.3±12.1)mmHg,64.7％ and 86.5％ in the combination therapy group ,respectively , and were (7.3±5.9)mmHg and (8.3±12.1)mmHg, 35.5% and 56.1% in the monotherapy group ,respectively .There were statisant difference between the combination therapy and the monotherapy groups in all the indexs (P<0.05).The fixed combination significantly reduced systolic blood pressure and diastolic blood pressur