Heavy metal concentrations in sea water are low, but their impacts on marine organisms are distinct. The effects in vitro of iron (Fe), copper (Cu), Zinc (Zn) and lead (Pb) on metalloenzymes (catalase and cytochrome oxidase) derived from Meretrix meretrix were measured in the experiment. The results showed that Meretrix meretrix accumulated Fe3+, Cu2+, Zn2+ and Pb2+ in various degrees, in which Fe3+ was strongly accumulated. The activity of CAT was obviously activated by the following elements within their specific ranges Fe3+ (2.0~13.0 mmol/L), Cu2+ (below 5.0 μmol/L), Zn2+ (below 10 nmol/L), Pb2+ (0.5~200 nmol/L). The activity of CCO was activated by Fe3+ and Cu2+ within their specific concentrations, Fe3+ (0.05~0.32 mmol/L) and Cu2+ (9.8~68.6 μmol/L). Zn2+ generally inhibited the activity of CCO even at the concentration as low as 1.0 nmol/L. The effects in vitro of iron (Fe), copper (Cu) and Zinc (Zn) on metalloenzymes (catalase and cytochrome oxidase) derived from Meretrix meretrix were different. Beyond a certain concentration range, these heavy metal ions could inhibit the activity of CAT and CCO to varying degrees, which probably contaminates the meretrix. ［Chinese Fishery Quality and Standards, 2014, 4(4):7-12］