The seeds of Zizyphus jujuta (=Z. vulgaris var. spinosus) have been used for treatment of insomnia, neurasthenia and neurosis in Korea and other parts of Asia. This drug is mild in effect and does not induce any drug dependence and tolerance on chronic administration. The early chemical investigations were the isolation of triterpenoids and saponins. We isolated a new C-glycosyl flavane named spinosin and its acylated derivatives, possessing some mild sedative activity. The structure of spinosin was elucidated as 2$quot;-O-β-D-glucosyl swertisin and three acylated derivatives were 6$quot;`-P-coumaroyl-, 6$quot;`-feruloyl and 6$quot;`-sinapoyl-spinosin. Swertisin itself was also contained in the seeds in a small quantity. The flavonoids were physiologically innocuous. The potentiatiated hexobarbital induced hypnosis, nomalized caffeine induced hyperactivity and decreased spontaneous movement. Although the flavonoids showed a rather weak activity compared with that of Zixyphus saponin according to our animal experiments, their very high content in the seeds presumably accounts for the assumption that they would play the leading role in pharmacological action of Zixyphus seeds.