Mangrove plants are distributed in the sea-shore, the river-mouth and the estuarial areas of the sub-tropical and tropical worlds which includes Okinawa, Japan. They are called halophyte pos sessingpeculiar physiological mechanisms for salt control. Of these mangrove plants, Rhizophor aceaehas viviparous seeds which form its next generations.<BR>For the first-step of a study on the mechanism of physiological process of mangrove plants, it was considered important to grasp the actual condition of their inorganic ions and organic acids.Therefore, an experiment was made in this study to select five kinds of viviparous seeds and Avicennia marina (not viviparous seed, but this species grows in the front area of the mangrove forest) and their calyx tubes, thereby analyzing their inorganic ions (cations and anions) and organic acids.<BR>The main inorganic ions contained in the viviparous seeds were sodium, potassium and chloride.In the upper parts of the viviparous seeds, there was indicated high concentration of soium and chloride. In the lower parts of the seeds, on the other hand, there was shown higher concentra tion of potassium than in the upper parts. Na/K ratio in the lower parts was found lower than in the upper parts.<BR>The main organic acids contained in the viviparous seeds were oxalic and malic acids. These organic acids were considered to have probably been used for neutralization of excessively absorbed cations.<BR>The main inorganic ions contained in the calyx tubes were sodium, potassium and chloride. Es pecially, they were found to have accumulated two to three times as much as the concentration in the Rhizophore parts (viviparous seed). Those various inorganic ions which passed through the root cell membranes were transported by the vessels to the seeds and other parts of the mangrove plant. Then, the calyx tube tissues of the viviparous seeds were supposed to accumulate those various inorganic ions (especially, sodium and chloride) excessively absorbed from the roots for the normal growth of the viviparous seeds.<BR>It was suggested by this study that an important point of the halophyte research was to know changes in the sap (cell sap) of the roots, stems, leaves and fruits (seeds) under saline conditions (sea water and brackish water). To make clear the reciprocal relations of ions and salts, therefore, future experiments will be made with an emphasis on an analysis of the ions of ionization of salt and intact salt in the plant sap.