The purpose of this study is to measure the changes of regional cerebral blood flow (rCBF) and blood pressure (BP) of Cortex Acanthopanacis in rats, and to determine the effect of Cortex Acanthopanacis on phenylephrine (PE) induced contraction of isolated rat thoracic aorta. The measurement was continually monitored by laser-doppler flowmeter (Transonic Instrument, USA) and pressure transducer (Grass, USA) in anesthetized adult Sprague-Dawley rats through the data acquisition system composed of MacLab and Macintosh computer. Contractile force was measured with force displacement transducer under 1.5 g loading tension. The result of this experiment was as following; 1. Cortex Acanthopanacis did not effect the changes of rCBF and blood pressure significantly. 2. Contractions evoked by phenylephrine were decreased significantly by Cortex Acanthopanacis 3. L-NNA, ODQ, atropine and indomethacin significantly altered the relaxation of Cortex Acanthopanacis. 4. Propranolol did not change the relaxation of Cortex Acanthopanacis. These results indicate that Cortex Acanthopanacis did not change the rCBF and BP, but Cortex Acanthopanacis can relax PE induced contraction of isolated rat thoracic aorta and that this increasing contraction related to endothelium and various mechanism.