Abstract: In order to explore seasonal variation of Microcystis community in Taihu Lake,water samples were collected at four representative sampling sites(River Mouth,Meiliang Bay,lake-bay intersection,and Center of Taihu Lake) in four seasons.Two methods,microscopic evaluation and PCR denaturing gradient gel electrophoresis(DGGE),were adopted to analyze the samples.The former did not find any significant seasonal variation of the dominant species(Microcystis aeruginosa,Microcystis wesenbergii and Microcystis flos-aquae) of the Microcystis community(P>0.05).However,the latter discovered that the Microcystis communities in the samples collected in summer and winter were separated into two feature groups,but those in the samples collected in spring and autumn were intermingled.Moreover,analysis show genetic distance of Microcystis in the same season was smaller than those in different seasons(P<0.01).In Taihu Lake,estival blooms consist mainly of Microcystis groups that are closely related.