This study aimed to evaluate the efficacy and safety of olmesartan medoxomil (OM)/amlodipine (AML) 20/5 mg fixed-dose combination tablet in Chinese mild to moderately hypertensive patients with inadequate blood pressure (BP) control on monotherapy. Two multicenter, randomized, double-blind, double-dummy, active-controlled, parallel group clinical trials were conducted. After screening and a 2-week placebo run-in period, patients with 95 mmHg ≤ seated diastolic blood pressure (SeDBP) < 110 mmHg received monotherapy with OM 20 mg (in Study 1) or AML 5 mg (in Study 2), once daily for 4 weeks. Patients with 90 mmHg ≤ mean SeDBP < 110 mmHg at the end of the monotherapy period were randomized to receive OM/AML 20/5 mg treatment or continue with the monotherapy, once daily for 8 weeks. OM/AML (20/5 mg) treatment significantly lowered both systolic and diastolic BP at 4 and 8 weeks compared to 40 mg olmesartan or 5 mg AML. The incidence of drug-related adverse effects did not differ significantly between the groups. OM/AML 20/5 mg was superior to OM 40 mg or AML 5 mg monotherapy in lowering BP in Chinese mild to moderately hypertensive patients with inadequate BP control on monotherapy. No new or unexpected safety issues were identified with OM/AML combination therapy compared to monotherapy.