The wormwood is one of the plants which occur widely throughout the world. Though the precise data on the entire chemical composition of mugwort leaves are not available, the major principles which have been found so far include inulin, alkaloid, thujon, sesquiterpene and several vitamins. Santonin, a parasiticide, is one of the glucosides extracted from the limited species of wormwood. It has long been known in herb medicine that the plants of this family has not only strong hemostatic, analgesic and parasiticidal actions but also therapeutic effects for diarrhea, stomachache and asthma. In recent pharmaceutical botany the wormwood is introduced to have antipyretic and astringent actions also. The mugwort(Artemisia asiatica Nakai) is the most common species of wormwood that occurs in Korea. The usage of this edible leaves of mugwort is rather various. It is used not only for wormwood bath but also as forage, moxa and medicinal agents. Recently Kim et al reported from their study on the effect of mugwort on the motility of isolated intestine of rabbits that tonus and motility were markedly enhanced by mugwort but this effect of mugwort on intestinal motility was almost completely blocked by atropine suggesting that activity of mugwort was exerted through its cholinergic effect. It was the findings of Kim et al that prompted the authors to do the present experiment. The present study was undertaken to investigate effects of mugwort(Artemisia asiatica Nakai) juice on the respiration and blood pressure in cats. And also studied was the mechanism of depressor action of Artemisia asiatica Nakai Juice (AAJ). The results obtained are as follows; 1) It was observed that mean arterial blood pressure and heart rate were decreased markedly by AAJ. Following administration of 0.15 ml/kg and 0.3 ml/kg AAJ into cats the maximum depressor responses observed were 77.5±2.2 mmHg and 94.0±3.7 mmHg respectively. 2) Depressor responses to AAJ were blocked markedly by atropine whereas the responses were not affected by propranolol and dibenamine. Therefore it is strongly inferred that depressor action of AAJ results mainly from its cholinergic effect. This inference was further substantiated by the fact that heart rate change which invariably accompanies depressor responses to AAJ was almost completely abolished by atropinization. 3) After administration of AAJ into cats frequency of respiration was markedly increased while depth of respiration decreased during first 2-3 seconds.