We tried to evaluate the activity of human glymphatic system by diffusion images. Our subjects were Alzheimer's disease (AD), in which it is known that the activity of the glymphatic system is impaired in animal experiments. We evaluated the diffusivity along the perivascular spaces as well as projection fibers and association fibers, and correlated them with MMSE score. There were significant positive correlation between diffusivity along perivascular spaces and MMSE score, indicating impaired water diffusivity related to AD severity. Our result may indicate that activity of the glymphatic system can be evaluated by diffusion images.