Abstract: The present study was designed to determine the spatial pattern of bacterioplankton community composition (BCC) in Lake Taihu in summer and to evaluate the relationship between trophic level and bacterial diversity. According to the survey conducted during August 2010, the bacterioplankton abundance significantly declined from the north and west of lake to the center and south, then to the east of the lake; and the changes were similar to the decline of the trophic levels in lake regions. In addition, Total phosphorus (TP) concentration but not total nitrogen (TN) was positively correlated with bacterioplankton abundance (R2=0.6392, n=29, P0.01; R2=0.0663, n=29, P0.05; respectively). Thus, P is a limiting factor for the growth of bacterioplankton in summer in Lake Taihu. A positive correlation between trophic level and bacterioplankton diversity in different lake regions was also observed in present study. Moreover, distinct spatial heterogeneity of BCC was observed in summer in Lake Taihu, which is mainly in accordance with the changes in trophic levels in various lake regions. Our study may contribute to better understanding of microbial loop and their ecological function in freshwater lakes.