Cultrichthys erythropterus is a common type of fish in Lake Taihu.Feeding habits of the fish were studied by analyzing 236 specimens from November 2004 to October 2005.The results showed that cladocerans and small fish were the dominant food items of C.erythropterus.Prey compositions of the fish varied in different fish body sizes.C.erythropterus longer than 130 mm in total length consumed more small fish, but that shorter than 130 mm-long mainly consumed cladocerans.In terms of feeding selec-tivity, C.erythropterus preferred Daphinia spp.and Limnoithona sinensis, but avoided copepodite, nauplius, Moina spp., Ceriodaphnia cornuta and rotifers.Thus the top-down effect of C.erythropterus varies with body sizes.The present paper also discussed the role of C.erythropterus in the ecosystem of Lake Taihu and made some suggestions for lake management and biomanipulation.