Abstract: The aim of this paper is to investigate the toxic effects of Pb²⁺ on the histopathological changes of gill and hepatopancreas in Tegillarca granosa exposed to four concentrations of Pb²⁺(5,15,45 and 90 μg/L).The experiment lasted for 96 hours.The results are as follows:for the groups of low Pb²⁺ concentrations,the gill isolated from the cartilage tissue,and for the groups of the high concentrations,the epithelia cells dropped,gill cavity swelled,which stored lots of haemocytes; finally the gill broke.The findings of gill ultrastructure showed that the number of secondary lysosome and mitochondrion increased.The influence of Pb²⁺ on the microstructure of hepatic cells only occurred in the groups of high concentrations,turning up some yellow sediment and a loss of dividing lines of the digestive tubules.Its ultrastructure results indicated that with the increasing metal concentrations,there was granular osmiophilic material,and the secondary lysosome increased as well; furthermore,the vacuoles were also present in the cytoplasm and nucleus of hepatic cells,suggesting the cells were irreversibly damaged.Combined with previous studies,we conclude that the histopathological alterations caused by heavy metals are not metal-specific but mainly because of oxidative stress.The antioxidant system is inferred to play a central role in the metal detoxification.