Because dementia is associated with both deterioration in the quality of life and poor prognosis, the prevention of cognitive impairment (CI) is a critical problem in public health promotion. Hypertension is a risk factor for the aggravation of CI, and the renin-angiotensin-aldosterone system (RAAS) is a key player in the increased incidence and development of hypertension. Therefore, the RAAS is considered to be a promoting factor for CI development. Conversely, recent studies have shown that lowering blood pressure with RAAS inhibitors decreases the incidence of CI, dementia and cardiovascular disease. Blood-brain barrier-penetrating RAAS inhibitors appear to have advantages in preventing cognitive decline because they can suppress the RAAS in the hippocampus, which has an important role in cognition. Thus, RAAS blockage is a notable strategy for preventing CI.