To evaluate the clinical efficacy and safety of a new angiotensin II type 1 receptor blocker, pratosartan, in patients with mild-to-moderate essential hypertension, a multicenter, open-label study was conducted. A 2- to 4-week run-in period was followed by a 12-week core study with pratosartan monotherapy, or a combination of pratosartan with a calcium channel blocker (CCB) or diuretic. Patients took a daily dose of 40, 80, or 160 mg pratosartan, with titration at 4-week intervals. Patients who tolerated pratosartan at the end of a 12-week core study then participated in a 9-month follow-up period (i.e., long-term study). Responder rates by pratosartan were 82.1% in the monotherapy, 81.3% in the combination with CCB, and 60.0% in the combination with diuretic group at 12 weeks. Pratosartan was efficacious throughout the long-term study, without serious adverse effects. Pratosartan significantly decreased serum total cholesterol in patients with hypercholesterolemia and uric acid in patients with hyperuricemia. In conclusion, pratosartan is an effective and well tolerated antihypertensive drug, and may have beneficial effects on hypertensive patients with some metabolic disorders.