FISH was used to analyze the abundance of dominated bacteria population in Meiliang Bay of Lake Taihu in winter andsummer in 2008. The four dominated bacteria population(a-proteobacteria,b-proteobocteria, y-proteobacteriu, Bacteroidetes) wereanalyzed by in situ hybridization with specific fluorescently(FITC) labeled rRNA-targeted oligonucleotide probes in the test. Theresults indicated;①The proportion of each of the four dominated species in the total number of bacteria was all significantly higherin winter than that in summer(P<0.01);②the abundance of a-proteobacteriu rose notably with the increase of TP concentration(R²=0.860, P<0.01);③there was ascending trend in the abundance of bacteria along with the increase of Chl. a concentra-lion,especially that of y-proteobocteria was more remarkable than the others (R²=0.857,P<0.01);④the abundance of bacte-ria population, especially for Bacteroidetes, was also influenced by PO₄^3---concentration(R²=0.733,P<0.05).