Disruption of BBB in AD has received increasing attention due to its potential role in amyloid accumulation and clearance. However, measurement of BBB leakage in AD has been proven challenging, especially when using non-contrast techniques. In this study, we measured BBB permeability to water in MCI patients using a novel technique that does not require any contrast agent. It was found that MCI patients have a higher permeability-surface-area-product (PS), i.e. leaky BBB, compared to elderly controls. Individuals with higher PS values had poorer cognitive performance and more severe vascular inflammation. These findings support the role of BBB disruption in AD.