Abstract: Objective To evaluate the efficacy and safety of amlodipine besylate plus losartan potassium and their interaction on the antihypertensive effect in patients with mild to moderate essential hypertension based on the factorial study design. Methods This was an 8-week, randomized, double-blind, factorial design, phaseⅡ, multicenter clinical study. A total of 299 patients with mild to moderate essential hypertension were included and were subsequently divided into 6 groups in a 1∶1∶1∶1∶1∶1 ratio. Patients in group A were treated with amlodipine besylate 5 mg simulant, losartan potassium 50 mg simulant, and losartan potassium 100 mg simulant. Patients in group B1 were administrated with losartan potassium 50 mg, amlodipine besylate 5 mg simulant, and losartan potassium 100 mg simulant. Losartan potassium 100 mg, amlodipine besylate 5 mg simulant, and losartan potassium 50 mg simulant were applied in patients in group B2. Patients in group B3 were treated with amlodipine besylate 5 mg, losartan potassium 50 mg simulant, and losartan potassium 100 mg simulant. Furthermore, patients in C1 group were administrated with amlodipine besylate 5 mg, losartan potassium 50 mg, and losartan potassium 100 mg simulant; meanwhile, the amlodipine besylate 5 mg, losartan potassium 100 mg, and losartan potassium 50 mg simulant were applied in the patients in C2 group. Sitting diastolic and systolic blood pressure and their changes were evaluated at 0, 4, and 8 weeks, respectively. Furthermore, adverse events were recorded. Results After 8 weeks of treatment, the changes in sitting diastolic blood pressure （-13.2±9.3） vs（-8.3±7.2） mmHg, F=-4.813, P＜0.001 and sitting systolic blood pressure （-19.9±15.5） vs（-11.9±14.3） mmHg, F=-4.550, P＜0.001 in the combination group（amlodipine besylate plus losartan potassium 5/50 mg and 5/100 mg, C1+C2 group） were more significant than those in the monotherapy group（B1+B2+B3 group）. According to the factorial analysis, amlodipine besylate 5 mg and losartan potassium 100 mg could affect sitting diastolic blood pressure and sitting systolic blood pressure at 8 weeks after treatment（all P＜0.05）. There was no interaction between these two drugs（both P＞0.1）. There was no difference in the incidence of adverse events among all groups（P=0.689）. Only one severe adverse event occurred in groups A（2.0%） and B3（2.1%） respectively. Conclusions The combination of amlodipine besylate and losartan potassium（5/50 mg and 5/100 mg） shows a better antihypertensive effect and does not increase the incidence of adverse events in patients with mild to moderate essential hypertension compared with the single drug regimen. Besides, no interaction effect is observed between them.