Abstract: 1. Suan-tsao-jen (酸棗仁) is the dried kernels of the fruits of Zizyphus spinosus Hu. It is used in Chinese medicine as a sedative and recommended especially in sleeplessness, whether from weakness or from pain. 2. A detailed account of their morphological and histological characters is made together with eleven plates of illustration. 3. After a careful comparison of Suan-tsao-jen with Tsao-jen (棗仁), it is proved that Tsao-jen is the kernel of the fruit of the plant, Zizyphus jujuba Mill. The distinguished pharmacognostical characters of Suan-tsao-jen and Tsao-jen are described in three tables. 4. The important diagnostic features of Suan-tsao-jen are as follows: (1) The palisade cells of the seed coat, up to 80 μ in length, with light line, the outer and the radial walls of which are considerably thickened. The radial walls show unequal thickening, the lower portions taper off to form thin-walls. (2) Nutritive layer, consisting of collapsed parenchyma cells with brownish content. Imbedded within the outer margin of this layer will be noted a few groups of parenchyma cells. (3) The inner seed coat, consisting of 1-2 layers of rectangular cells with beaded walls. (4) Endosperma, consisting of irregular thin-walled cells, up to 35 μ in length, containing aleurone grains and oil globules. (5) Mucilaginous zone of endosperma, 20-30, μ in width. (6) The rectangular epidermis cells of cotyledone, up to 25 μ in length. containing calcium oxalate in rosette aggregates about 3μ in diameter. The mesophyll cells of the cotyledons are elongated and contain oil globules and aleulone grains.