The glymphatic system is a waste clearance pathway in brain. During sleep, the increase in the interstitial influx results in faster waste removal. Apparent diffusion coefficient (ADC) in brain significantly changed during the cardiac cycle, and this change (ΔADC) shows the degree of fluctuation in water molecules. Therefore, we analyzed fluctuation of water molecules in the brain of healthy subjects in awake and sleep states. Maximum ADC and ΔADC of the white matter increased in sleep state. Fluctuation analysis facilitates the noninvasive evaluation of the dynamic state of water movement in the brain in sleep state as a glymphatic MRI.