Fructus Tribuli has been used in Korea for many centuries as a therapeutic agent for headache and dizziness due to hyperactivity of the liver-yang. The effect of Fructus Tribuli on the blood pressure is not known. The purpose of this study was to determine the effect of Fructus Tribuli on blood pressure and artery rats and rabbits. 1. Fructus Tribuli exerted a dose-dependent relaxation of isolated rabbit common carotid artery. 2. Blood pressure was significantly decreased by Fructus Tribuli (10.0mg/kg) in rats.