The purpose of this study is to evaluate of efficacy and safety of amlodipine plus losartan and losartan alone in patients with essential hypertension inadequately controlled on losartan monotherapy.

Inclusion Criteria:

• Patients over 18 years of age
• Essential hypertensive patients whose blood pressure is not controlled before the study (sit DBP≥90 mmHg for drug-treated patient, sit DBP≥95mmHg for drug-naïve patient)
• Non-responder to 4 weeks treatment of losartan 100 mg monotherapy (sit DBP≥90mmHg)

Exclusion Criteria:

• mean sit SBP≥200mmHg or mean sit DBP≥120mmHg at screening
• mean sit SBP≥180 mmHg or mean sit DBP≥120mmHg after 4 weeks of losartan 100mg treatment
• has a history of hypersensitivity to dihydropyridines or angiotensin II receptor blockers
• Secondary hypertensive patient or suspected to be
• Uncontrolled diabetes mellitus patients
• Severe heart disease or severe neurovascular disease
• Known as severe or malignant retinopathy
• Patients showed clinically significant hematological finding, patients with renal diseases (serum creatinine), patients with hepatic disease (ALT or AST)
• History of malignancy tumor
• History of autoimmune disease
• History of alcohol or drug abuse
• Positive to pregnancy test, nursing mother, has an intention on pregnancy
• Considered by investigator as not appropriate to participate in the clinical study with othe reason