ADC of the brain significantly changes during the cardiac cycle because of intracranial pressure changes and fluid fluctuations. We hypothesized that ADC of the brain changes during the respiratory cycle because intracranial pressure changes during the respiratory cycle. We determined the maximum and minimum ADC (ADCmax and ADCmin) and maximum change in ADC (ΔADC) in the respiratory cycle and non-synchronized periodical data. ADCmax and ΔADC in the white matter with respiratory-synchronization were significantly greater than those with non-synchronized periodical scan, whereas there was no significant difference in ADCmin between the scans. ADC of the brain changes during the respiratory cycle.