Abstract:Ecological adaptation and ecological group of Thaliacea were examined in the East China Sea (23°30′-33°00′N, 118°30′-128°00′E), in relation to temperature and salinity. The data were collected in 4 surveys conducted from 1997 to 2000. The Yield Density Model was used to predict optimum temperature and salinity of water for Thaliacea occupations. Furthermore, the optimum temperature (salinity), average appearance temperature (salinity), and scatter diagrams of temperature-abundance for the species of Thaliacea were used to predict the distribution of the species. Then coupling the biogeographical information, the ecological group of Thaliacea were identified as follows: Salpa fusiformis was thought as a offshore and temperate warm water species, Cyclosalpa pinnata polae and Ritteriella amboinensis are oceanic and tropical species, the other 13 species, Thalia decocratica orientalis, Doliolum denticulatum, Dolioetta gegenbauri, Weelia cylindrica, Cyclosalpa pinnata, Thalia decocratica, Ritteriella picteti, Brooksia rostrata, Cyclosalpa pinnata f. quadriluminis, Doliolum nationalis, Thalia rhomboides, Cyclosalpa floridana and Pyrosoma atlanticum are offshore and subtropical water species. Salpa fusiformis was common found in side of higher salinity (32.06-34.77) where East China Sea Coast Current met and ECS Mixed water mass. Cyclosalpa pinnata polae tends to distribute along the waters between 100m and 200m isobath, where the Taiwan Warm Current locates so that the species can acts as an indicator species of the Taiwan Warm Current. The high abundance areas of Thalia decocratica orientalis can indicate the location where the coastal water mixed with Kuroshio when it intrudes into continental shelf water in the East China Sea.