Diospyros Kaki Thunberg is the species of persimmon tree that grows in Korea. Although its fresh or dried fruits are often served as a desert, it has little been known if persimmon tree has any specific pharmacological action. The leaves and branches of persimmon tree has long been used as folk remedies for palsy and frostbite in the southern part of Korea and it is also in use for the treatment of hiccup and nocturnal enuresis in chinese herbal medicine. Recently it was reported that an intravenous administration of Diospyros Kaki Thunberg ethanol extract (KTEE) into the animals lowered arterial blood pressure. Lee concluded from his study on the mechanism of depressor action of KTEE that at least a part of depressor response he observed was caused by acetylcholine-like action of KTEE. On the other hand little study has been made on the effect of KTEE on the motility of isolated animal intestines. Therefore the present study was undertaken to investigate effect of KTEE and the mechanism of its action on the motility of isolated rabbit duodenum. Ethanol extract of Diospyros Kaki Thunberg was prepared by boiling 1 kg of dried branches of persimmon tree in 1 liter of ethanol and the motility of isolated rabbit duodenum was recorded on physiograph by means of force transducer connected with Magnus apparatus. Doses of KTEE used were 5 X 10^-4 gm/ml, 1 X 10^-3 gm/ml, and 2 X 10^-3 gm/ml. And the isolated duodenum was separately pretreated with acetylcholine (5 X 10^-7 gm/ml), pilocarpine (2.5 X 10^-6 gm/ml), histamine (5 X 10^-6 gm/ml) and barium chloride (2.5 X 10^-5 gm/ml) in order to find out interactions of these drugs with KTEE. The results obtained are as follows: 1. At doses of 5 X 10^-4 gm/ml, 1 X 10^-3 gm/ml KTEE reduced contractions of isolated duodenum, while tonus as well as contaction of duodenum were depressed with 2 X 10^-3 gm/ml of KTEE. 2. Since the inhibitory effect of KTEE on the intestinal motility was not blocked by pretreatment with acetylcholine, pilocarpine, and barium chloride, it was strongly suggested that the inhibitory action of KTEE on intestinal motility is mainly Caused by its antihistamine effect. 3. It is also concluded that the principal substance of KTEE responsible for inhibition of intestinal motility may also have a vasodilating activity and would not be an acetylcholine-like substance in case it is same substance as that cause depressor responses.