A comprehensive survey on the community structure of protozoa was conducted in Mingzhu Lake of Chongming Island in each month of 2008.The protozoa was collected and identified using freshwater plankton survey methodology,and the type of protozoa distribution,community structure,species composition,dominant species and species diversity were analyzed.The results showed that there were 60 species of protozoas in Mingzhu Lake,belonging to 3 classes,26 genera.The dominant species were Peridinium bipes,Euglena caudate,E.geniculata,Strombidium viride,Gymnodinium aeruginosum,Tintinnidium evtzii,Euplotes sp.The average annual density of protozoa was(42 075±21 594)ind/L and the average annual biomass was(1.531±1.384)mg/L.The Shannon-Wiener diversity,evenness index and richness index of the protozoa community in the Lake were relatively low.The relationship between species diversity index and the quality of water was closely correlated.In the functional nutrition taxa of protozoa,the proportion of algivores and bactivores-detritivores were higher than the photosnthetic qutotrophs and raptors.The significant factor affecting protozoa distribution was temperature,Chl.a content,TN and TP which suggested that the Mingzhu Lake was moderately polluted.