Abstract: On the basis of data of four seasonal investigations in the East China Sea(23°30'～33°00'N,118°30'～128°00'E) in 1997~2000,the distribution and the seasonal variation of Pteropods abundance and the environmental factors on Pteropods abundance as well as the regression contribution of the abundance of dominant species to total abundance were discussed through qualitative and quantitative methods.Results show a clear seasonal change of Pteropods abundance with the following order:autumn(108×10^-2～500×10^-2ind/m³) being greater than summer(33×10^-2ind/m³) being greater than winter(28×10^-2ind/m³) beingg reater than spring(10×10^-2ind/m³).Pteropods were not observed in north shallow waters of the East China Sea(29°30'~33°N,123°30'~125°E) in winter and spring.The seasonal changes of Pteropods show that the Pteropods abundance in the south is higher than that in the north and that in the out shore higher than that in the off shore.On the basis of the analysis results of dominance and regression contribution,the Pteropods abundance distribution is decided mainly by the distribution of Creseis acicul a in spring,C.virgula in summer,Desmopterus papilio in autumn and Limacinat rochi formis in winter.The variation of Pteropods abundance shows a clear linear correlation with surface water temperature and 10 m water temperature but no significant correlation with bottom water temperature or salinity.In summer,the high-abundance distribution area of Pteropods is located in the place where the Taiwan Warm Currentorig inates from Kuroshio.In autumn,the distribution area with abundance higher than 250×10^-2ind/m³ expands with the Taiwan Warm Current north ward within the mixing area where the Changjiang fresh water,the Zhejiang-Fujian coastal water and the cold water of Huanghai Sea meettogether.Water temperature and warm currents are the mostimportant environmental factors that influenced the changes of Ptero pods abundance in the East China Sea.