The occurrence,toxicities,and ecological risks of five heavy metals (Pb,Cu,Cd,Zn and Ni) in the sediment of Taihu Lake were investigated in this study.To evaluate the toxicities caused by the heavy metals,the toxicities induced by organic contaminants and ammonia in the sediments were screened out with activated carbon and zeolite.The toxicities of heavy metals in sediments were tested with benthic invertebrates (tubificid and chironomid).The correlations between toxicity of sediment and the sediment quality guidelines (SQGs)derived previously were evaluated.There were significant correlations (p ＜ 0.0001) between the observed toxicities and the total risk quotients of the heavy metals based on SQGs,indicating that threshold effect level (TEL) and probable effect level (PEL) were reliable to predict the toxicities of heavy metals in the sediments of Taihu Lake.By contrast,the method based on acid volatile sulfides (AVS) and simultaneously extracted metals (SEM),such as ∑SEM/AVS and ∑SEM-AVS,did not show correlations with the toxicities.Moreover,the predictive ability of SQGs was confirmed by a total predicting accuracy of 77％.Ecological risk assessment based on TELs and PELs showed that the contaminations of Pb,Cu,Cd and Zn in the sediments of Taihu Lake were at relatively low or medium levels.The risks caused by heavy metals in the sediments of north bay of the lake,which received more wastewater discharge from upper stream,were higher than other area of the lake.