This preliminary study investigated cognition associated cerebral perfusion changes in Alzheimer’s disease (AD) and mild cognitive impairment (MCI) measured with a novel 3D arterial spin labeling technique. The voxel-wise regression analysis against MMSE scores was performed using whole brain CBF maps. Cognition associated CBF deficits in the hippocampus and insular cortex might cause the typical AD symptoms including memory loss and emotion issues. CBF decrease in MCI patients in the lingual gyrus could affect vision and wording functions. CBF increase in the frontal lobe might serve as an early indicator for high-level cognitive function disturbance.