Zizyphus seed(Zizyphus vulgaris Lamark var. Spinosus Bunge) has long been used as hypnotics and sedatives in oriental medicine, and it is reported that the Zizyphus seed elicited a variety of pharmacologic actions besides CNS depression. Present study was undertaken to investigate the effects of Zizyphus seed on the central nervous system and on the blood pressure. The effect of Zizyphus seed on the central nervous system was measured by the influence of thiopental sleeping time and by inhibition of chemical convulsion (strychnine and pentylenetetrazol induced). Blood pressure changes by Zizyphus extract and its mode of action were investigated. The ground Zizyphus seed was extracted with hexane and methanol, consecutively and the supernatants were discarded. The precipitate was re-extracted with distilled water and the supernatant was evaporated to a dark-brownish sticky liquid, which was used as Zizyphus seed extract in this study after dissolving in saline prior to experiment. The results are as follows. 1) Zizyphus seed extract caused marked prolongation of the thiopental sleeping time in mice. 2) The chemical convulsion by strychnine and pentylenetetrazol, and the mortality by them in chicks were not affected by pretreatment of Zizyphus seed extract. 3) Zizyphus seed extract produced transient fall of blood pressure in the cat, and this hypotentive effect was blocked partially by atropine but not affected by bilateral vagotomy and/or hexamethonium, nor propranolol and, chlorpheniramine and/or cimetidine. With the above results, it may be suggested that the water extract of Zizyphus seeds contains components producing CNS depression and hypotension. Furthermore it is felt that the cholinergic effect, but not the adrenergic or histaminergic, is partly responsible for the hypotensive effect of Zizyphus seed extract.