The vertical distribution of radiolarian faunas on September 28, 2005 and the temperature, salinity, density, and fluorescence intensity profiles are documented from surface and subsurface waters (> 100m deep) in the Japan Sea, off Tassha, Sado City, Sado Island, Niigata Prefecture, central Japan. The features of the water mass structure shallower than 100m deep are distinguished by gentle gradients of temperature and salinity in waters between 100m and 20m deep (the lower layer: LL) and a homogeneous temperature and salinity (24.0℃, 32.9psu) in waters shallower than 20m (the upper layer: UL). The species composition of the deeper fauna (ca. 77-54m) is characterized by the abundant occurrence of Acanthosphaera actinota, Pseudocubus sp. A, Lophospyris sp., and Acanthodesmia sp. It is also noteworthy that each species in the deeper water fauna does not exceed 20％. In the shallower fauna (ca. 35-0m), Spongosphaera streptacantha, Pseudocubus obeliscus, and Pseudocubus sp. A comprise 87.5％ of the fauna. Considering the characteristics of vertical water properties, high standing stocks of these three species are likely caused by their temperature preferences and adaptive strategies for a summer environment in the Japan Sea. There is a slight difference in species composition between September faunas of 2000 and 2005 which is probably related to the Tsushima Warm Current (TWC). It is known that the flow force of the TWC varies in 2 to 3- and 10-year cycles, so the TWC fluctuation may influence the annual variation of the fauna around Sado Island.