Citrus unshiu Marc., a family of Rutaceae, has been used as antitussives, antiemetics, expectorants, spasmolytics, stomachics and digestants in oriental medicine. But there is few reports on the pharmacological effects of Citrus unshiu pericarpium. Present experiment was performed to observe the effects of the water extract of Citrus unshiu on isolated auricle and intestine in rabbits and blood pressure in rats and also to study on the active component on the cardiovascular system by means of thin layer chlomatography and spectrophotometer. 1. The water extract showed positive inotropic and positive chronotropic effect in the concentration of 1 X 10^-4g/ml, 5 X 10^-4g/ml, and 1 X 10^-3g/ml. 2. The motility of isolated rabbit intestine was significantly depressed by the water extract. 3. The blood pressure was markedly increased by the water extract. 4. The blood vessel of rabbit ear was constricted by perfusion of the ether extract. 5. The purified alkaloid of Citri pericarpium by ion exchange resin showed the same Rf value with l-synephrine on thin layer chromatography. 6. The purified alkaloid of Citri pericarpium by thin layer chromatography showed the same absorption curve with l-synephrine in the ultraviolet scanning.