Background Arterial stiffness is associated with cognitive decline and dementia; however, the precise mechanisms by which it affects the brain remain unclear. Methods and Results Using a mouse model based on carotid calcification this study characterized mechanisms that could contribute to brain degeneration due to arterial stiffness. At 2 weeks postcalcification, carotid stiffness attenuated resting cerebral blood flow in several brain regions including the perirhinal/entorhinal cortex, hippocampus, and thalamus, determined by autoradiography ( P <0.05). Carotid calcification impaired cerebral autoregulation and diminished cerebral blood flow responses to neuronal activity and to acetylcholine, examined by laser Doppler flowmetry ( P <0.05, P <0.01). Carotid stiffness significantly affected spatial memory at 3 weeks ( P <0.05), but not at 2 weeks, suggesting that cerebrovascular impairments precede cognitive dysfunction. In line with the endothelial deficits, carotid stiffness led to increased blood‐brain barrier permeability in the hippocampus ( P <0.01). This region also exhibited reductions in vessel number containing collagen IV ( P <0.01), as did the somatosensory cortex ( P <0.05). No evidence of cerebral microhemorrhages was present. Carotid stiffness did not affect the production of mouse amyloid‐β (Aβ) or tau phosphorylation, although it led to a modest increase in the Aβ40/Aβ42 ratio in frontal cortex ( P <0.01). Conclusions These findings suggest that carotid stiffness alters brain microcirculation and increases blood‐brain barrier permeability associated with cognitive impairments. Therefore, arterial stiffness should be considered a relevant target to protect the brain and prevent cognitive dysfunctions.