Concentration and distribution of 19 organochlorines and 6 heavy metals in the surface sediment of southern Lake Taihu were studied and the relevant risk assessment was carried out.The results showed the concentrations of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) detected ranged from 0.51-4.98ng/g(dw) and 1.49-15.15ng/g(dw),respec-tively,which was at a low contamination level compared to other fresh water sediments in China.The congener of α-hexachlorocy-clohexane (α-HCH) was the dominant pollutant among OCPs and CB194,and CB28 were the dominant PCBs.The concentration rangesof Cu,Zn,Cr,Ni,Pb and Cd in the surface sediments of southern Lake Taihu were 14.4-79.7mg/kg,69.3-214mg/kg,65.0-99.5mg/kg,24.8-48.7mg/kg,12.3-39.2mg/kg and 0.015-0.563mg/kg,respectively.Effects range low (ERL) and effects range median (ERM) were used to evaluate the ecological risk of organochlorines.It was found that 90% of the sampling sites had a dichlorodiphenyltrichloroethanes (DDTs) value lower than the ERL,and the γ-HCH and PCBs values of all sites were lower than the ERL.The risk assessment was completed on heavy metals in sediments by using the potential ecological risk index (RI).The results indicated that the overall ecological risk caused by heavy metals was low.The potential ecological risk index of Cd was relatively higher,and the RIs of several heavy metals in XMK-0 were relatively higher than that in other sites.Al-though the concentration levels of the above organochlroine and heavy metal pollutants in the surface sediments of southern Lake Taihu were low and no serious threat has been observed to the ecological system,the prevention to these contaminations should not be ignored for their accumulative effect and toxicity in the environment.