To investigate the efficacy and safety of azilsartan compared to olmesartan medoxomil in patients with grade I or II essential hypertension

Inclusion Criteria:

1. Both sexes. eighteen years or older and no more than 70 years at the time of informed consent

2. Grade I or II essential hypertension

3. Both sitting systolic and diastolic blood pressures at Week 0 during the run-in period meet the following criteria:

   Sitting systolic blood pressure: greater than or equal to 150 mmHg and less than 180 mmHg

   Sitting diastolic blood pressure: greater than or equal to 95 mmHg and less than 110 mmHg

4. Able to understand the content of the study and comply with the study and to give informed consent in writing before participating in the study

Exclusion Criteria:

1. Secondary hypertension, grade III hypertension (sitting systolic blood pressure greater than or equal to 180 mmHg or sitting diastolic blood pressure greater than or equal to 110 mmHg), or malignant hypertension，hypertensive emergencies，hypertensive urgencies
2. The following circulatory-related diseases or symptoms:

(1) Cardiac disease: angina pectoris; valvular stenosis; atrial fibrillation; the following diseases requiring medication: congestive heart failure or arrhythmia； (2) Cerebrovascular disorder: cerebral infarction, cerebral hemorrhage (onset within 24 weeks before start of the screening period), transient ischemic attack (onset of an attack within 24 weeks before start of the screening period)； (3) Vascular disease: arteriosclerosis obliterans with symptoms of intermittent claudication； (4) Progressive hypertensive retinopathy: hemorrhage, exudation, or papilledema (observed within 24 weeks after start of the screening period)

3. Decrease in sitting diastolic blood pressure by 8 mmHg or more at the end of the run-in period (Week 0) compared to the start of the screening period

4. Day/night reversal, e.g., nightshift worker

5. Unilateral or bilateral renal artery stenosis

6. Clinically apparent hepatic and renal impairment (e.g., with AST and ALT values of 2.5 x upper limit of normal or higher, with serum creatinine value of 1.5 x upper limit of normal or higher during the screening period)

7. Hyperkalemia (with a laboratory value of 5.5 mEq/L or higher during the run-in period)

8. Malignant tumor

9. Compliance with the study drug of less than 80% during the run-in period

10. Poorly-controlled diabetes mellitus (fasting plasma glucose greater than 11mmol/L)，and/or complications (kidney disease, peripheral neuropathy) at Screening.

11. History of hypersensitivity or allergy to olmesartan medoxomil tablets and related drugs (ARB, ACE inhibitors, and renin inhibitors)

12. History of drug abuse (defined as illegal drug use) or alcohol dependency within 2 years before start of the screening period

13. Requirement of the excluded treatment

14. Pregnant or lactating women

15. Participation in another clinical trial or post-marketing clinical trial within 30 days before start of the screening period

16. Dangerous machinery operator such as aerial worker，motor vehicle driver