Objectives: Uwhangchungsim-won (DC) has been used in various medical fields such as stroke, hypertension, atherosclerosis, autonomic imbalance and mental instability, etc. The aim of this study was to evaluate the effect of UC on cerebral hemodynamics and estimate the appropriate dose of UC. Methods: We studied changes of hyperventilation-induced cerebrovascular reactivity and mean blood flow velocity of middle cerebral arteries (MCA) using transcranial Doppler. We observed the changes of mean blood pressure, pulse rate and expiratory CO2 using S/5 Compact Anesthesia Monitor from 10 healthy young volunteers who were administered UC twice a day in the 1 st section and then once a day in the 2nd section. Results: Mean blood pressure tended to decrease at 1 hour and pulse rate tended to decrease at 2 hours after second administration. After 2 hours, mean blood pressure rose to state before administration, but pulse rate maintained from 2 hours to 4 hours. The changes were not statistically significant. Cerebral blood flow velocity in middle cerebral artery was not statistically significant after second administration. Cerebrovascular reactivity increased from 2 hours to 4 hours after second administration. Conclusions: This study provides that administration of UC twice a day is more effective on hyperventilation-induced cerebrovascular reactivity than administration of UC once a day.