In order to elusidate the distribution of modern dinoflagellate cysts around the Japanese Islands, several surface sediments were analized in palynological procedure. The samples were collected from Nagasaki Bay, Omura Bay, Senzaki Bay, Lake Hiuga, Lake Kamo, off Honjo, and off Oga in the coastal areas of the East China Sea and the Sea of Japan, and also strongly influenced by the Tsushima Warm Current which is a branch of the Kuroshio Current.<br>The species of the dinoflagellate cysts identified are listed in Table 2. They consist mainly of the Gymnodinioid, Gonyaulacoid, Tuberculodinioid and Peridinioid Leneages.<br>The characteristics of the modern dinoflagellate cyst assemblages along the near-shore areas of the East China Sea and the Sea of Japan are as follows.<br>1) The relative frequency of the genus Spiniferites belonging to the Gonyaulacoid Lineage decreases with going up north of the Tsushima Current. On the contrary, that of the genus Brigantedinium assignable to the Peridinioid Lineage increases with it (Text-fig. 3).<br>2) The species mainly constituting the genus Spiniferites are Spiniferites bentori (ROSSIGNOL), Spin. bulloideus (DEFLANDRE & COOKSON), Spin. aff. delicatus REID, and Spin. mirabilis (ROSSIGNOL).<br>3) Tuberculodinium vancampoae (ROSSIGNOL) of the Tuberculodinioid Lineage and cyst of Polykrikos hartmannii ZIMMERMANN of the Gymnodinioid Lineage are dominant in the samples of the southern area of the Tsushima Current region. Operculodinium centrocarpum (DEFLANDRE & COOKSON) assignable to the Gonyaulacoid Lineage is relatively abundant in the nothern area.<br>For clarifying the species diversity of the modern dinoflagellate cysts, the FISHER'S species diversity (α) is calcurated on each area of the Tsushima Current region, and several areas of the western coastal parts influenced by the warm Gulf Stream in the north Atlantic Ocean (Table 3). The higher values of α (6.0-5.5) are distributed in such southern areas of the Tsushima Current region as Nagasaki Bay, Omura Bay and Senzaki Bay. The species diversity in this region possibly indicates the positive interrelation with the surface water temperature of both winter (February) and summer (August). This is due to the Tsushima Current going upnorth. The similar relation between the water temperature and the species diversity is also observed in the coastal area of the Gulf Stream in the northern Atlantic.<br>According to these data, the distribution of the modern dinoflagellate cysts in surface sediments is generally controlled by the surface water temperature.