Abstract: The root of Veratrum mengtzeanum, the Chinese medicinal plant "Li-Lu" was extracted by a modified Cramer's method. Our investigation was carried out on cats and rabbits under urethane anesthesia. Intravenous injections of 0.1—0.15 gm/kg produced a prompt fall of arterial blood pressure with an average reduction of 68% for cats and. 38% for rabbits. In the lapse of 1—2 hours, the blood pressure gradually recovered. Repeated administrations revealed no tachyphylaxis. The fall of blood pressure was, as a rule, accompanied by bradycardia, respiratory depression, and sometimes, apnea (Bezold effect). The mechanism of the hypotensive effect of the drug was due to the action on the receptors of carotid sinus, heart, and lungs, which induced reflexly a fall of blood pressure. It was ascertained by the following facts: The hypotensive effect was clearly diminished by either vagotomy or denervation of the carotid sinus. After denervation of carotid sinus and vagotomy, the drug produced an increase of blood pressure. V. mengtzeaum could possibly possess also a direct stimulating action on the central nervous system. In the experiments on perfusing isolated cat's hind limb, the drug had no effect on the outflow. On rabbit's heart in situ the drug increased the contraction amplitude. In mice the oral acute LD₅₀ was found to be 20 ± 3 gm/kg. Respiratory depression and fine tremor somewhat like shivering were noticed.