Abstract: The effects of heavy metal ions(Cu2+,Pb2+,Zn2+ and Ag+)on N-Acetyl-β-D-glucosaminidase from Eriocheir sinensis were studied.The results showed that Cu2+,Pb2+ and Zn2+ inhibited the activity of enzyme in vary degree.Cu2+ and Zn2+ were both reversible non-competitive inhibitors.The inhibition constants of free enzyme(KI) of Cu2+ and Zn2+ were 1.25 mmol/L and 8.10mmol/L,respectively.Pb2+ was reversible mixed-type inhibition.The inhibition constants of free enzyme(KI) and enzyme-substrate complex(KIS) of Pb2+ were determined to be 10.44mmol/L and 2.18mmol/L,respectively.Ag+ activated the enzyme at low concentrations,but it inhibited the enzyme at higher concentrations as a reversible un-competitive inhibitor.The inhibition constants(KIS) was 204.51mmol/L.