Angiotensin receptor blocker (ARB)/hydrochlorothiazide (HCTZ) combination therapy has been shown to produce a prompt reduction in clinic blood pressure (BP) without serious adverse effects; however, long-term antihypertensive efficacy on home BP has not been fully investigated. In this open-label multicenter observational study, a total of 151 hypertensive patients uncontrolled with antihypertensive regimens including standard dose of ARBs were switched to the fixed-dose combination of losartan (50 mg)/HCTZ (12.5 mg) (mean age 66.9 ± 9.5 years, 51% male, 19% with diabetes mellitus, and 57% with dyslipidemia). After 3 months, losartan/HCTZ treatment significantly reduced mean home systolic BP/diastolic BP from a baseline level of 153 ± 11/85 ± 9 mm Hg to 136 ± 12/77 ± 10 mm Hg (P < .001) and mean clinic BP from 158 ± 9/87 ± 9 to 136 ± 12/77 ± 10 (P < .001), which were maintained through the study period of 12 months (132 ± 11/75 ± 9 and 136 ± 12/77 ± 10; home and clinic BP at 12 months, respectively, P < .001). Furthermore, younger patients (< 65 years) receiving ARB monotherapy at the start of the study showed a significantly greater reduction in home BP, but not in clinic BP, compared with elderly patients (≥ 65 years). In conclusion, losartan/HCTZ combination therapy exerted a 1-year long-term efficacy on home BP as well as clinic BP. In patients uncontrolled with ARB monotherapy, the antihypertensive efficacy on home BP is more pronounced in younger patients compared with that in elderly patients.