The purpose of this study was to measure the changes of regional cerebral blood flow(rCBF) and blood pressure(BP) in rats, following the intravenous injection of Flos Sophora japonica L.(FSJ) water extract. The measurement was continually monitored by Laser-Doppler Flowmeter and pressure transducer in anaesthetized adult Sprague-Dawley rats for 2 hours to 2 hours and a half through the data acquisition system. FSJ increased the changes of rCBF in rat significantly. The rCBF of FSJ did not change by pretreated propranolol, atropine, L-NNA($N^G$-nitro-L-argininine) and indomethacin. But the rCBF of Flos Sophora japonica L. was increased by pretreated methylene blue. FSJ decreased the changes of BP, significantly. The BP of FSJ did not change by pretreated propranolol, atropine, L-NNA and indomethacin. But the BP FSJ was decreased by pretreated methylene blue. There results indicated that FSJ can increase the rCBF and decrease the BP, that is related to guanylyl cyclase activity.