Seasonal variations in rotifers of the waters with diR'erent eutrophication states(the open water area,Meiliang Bay, Iske Wulihu) in Iake Taihu were studied during Oct. 2003-Sep. 2004. The concentration of nutrients was the highest in lake Wulihu and lowest in the open water area. The species number and biomass of rotiferswere the highest in lake Wulihu and lowest in the open water area. Regression analysis suggested that there was asignificant positive correlation between the number of rotifers and the concentration of TN and Chl. a; and the biomass of rotifers was also significantly correlated to the concentration of Chl. a. The study indicated that the structureof rotifer was significantly different among the three areas in lake Taihu. It also suggested that eutrophication hadsignificant effect on the structure of rotifer community in lake Taihu.