In Japan, ambulatory blood pressure monitoring (ABPM) became covered by health insurance in April 2008. In The Japanese Society of Hypertension Guidelines for the Management of Hypertension (JSH2009), the importance of 24-h blood pressure monitoring was also described in an additional section. Therefore, ABPM may be increasingly applied in hypertension treatment. However, in Japan, few studies have presented data on the effects of various anti-hypertensive agents on 24-h blood pressure changes. Irbesartan became commercially available in July 2008 as the sixth angiotensin II type 1 receptor blocker in Japan. In the present study, 24-h blood pressure control was examined using ABPM in Japanese patients with essential hypertension who were treated with irbesartan, and its efficacy was evaluated. This study was completed in 30 of the 32 subjects. This agent decreased both the nocturnal and daytime blood pressures and reduced the rate of change in the systolic blood pressure early in the morning, resulting in favorable blood pressure control. It also significantly decreased the urinary albumin level, suggesting that it exhibits renoprotective effects at doses approved in Japan.