Abstract: Virioplankton,viruses in aquatic ecosystem,are now considered to be an abundant and dynamic component in the aquatic microbial communities that can regulate the biomass production and species composition of heterophic bacteria,cyanobacteria,and phytoplankton,influence biogeochemical cycling,and mediate gene transfer between microorganisms in aquatic ecosystems.Lake Donghu located in Wuhan city was a eutrophic shallow lake,which contains three trophic regions:hypereutrophic,eutrophic and mesophic region. To assess the ecological role of virioplankton in Lake Donghu,it is necessary to determine the abundance and the morphotype diversity of virioplankton. The virioplankton abundance was measured by transmission electron microscopy (TEM) direct counts and epifluorescence microscopy (EM) direct counts using SY BRG old stain in Lake Donghu. All data were analyzed by SAS811 (SATA) software packages (SAS Institute Inc.). Water column virioplankton abundances were revealed highest numbers (9.74 × 108mL-1) in eutrophic region and lowest numbers(7.68 × 108mL-1) in mesotrophic region by TEM.Virioplankton direct counts of hypereutrophic and eutrophic regions were significantly higher (P <0.05) than those of mesotrophic region.Virioplankton abundances counted by EMwere significantly higher than those counted by TEM (P <0.01),up to 2.72 times on average. The analysis of morphological diversity of virioplankton by TEM showed that most virioplankters observed were similar to bacteriophages and cyanophages which had diverse tails and hexagonal heads. According to morphotype,most of them belong to Siphoviridae (Tail is noncontratile,long),Myoviridae (Tail is contractile,long and complex,consisting of a central tube and a contratile sheath separated from the head by a neck) and Podoviridae (Tail is short about 20 nm and noncontratile). In addition,filovirus,baculovirus,bullet2shaped virus,rod-shaped virus, and other viruses,were also detected. Some virus-like particles observed with clear capsomer were similar to human and animal virus. In water samples,virioplankton abundance detected was much more than those of bacterioplankton,cyanobacteria and algae. The results suggest that virioplankton played vital roles in water environment and ecosystem of Lake Donghu.