The study was designed to investigate the effects of Leonuri herba extract (LHE) on the change of regional cerebral blood flow (rCBF) and mean arterial blood pressure (MABP) in normal rats, and further to determine the mechanism of action of LHE. The results in normal rats were as follows, LHE significantly increased rCBF in a dose-dependent manner, and MABP did not change in a dose-dependent manner. This results were suggested that LHE significantly increased rCBF by dilating pial arterial diameter. The LHE-induced increase in rCBF was significantly inhibited by Pretreatment with indomethacin(1 mg/kg, i.p.), an inhibitor of cyclooxygenase, and was significantly inhibited by methylene blue($10{mu}g/kg$, i.p.), an inhibitor of guanylate cyclase. The LHE-induced MABP did not change by pretreatment with indomethacin but was significantly inhibited by methylene blue. This results were suggested that the mechanism of LHE was mediated by cyclooxygenase.