Austenite antibacterial stainless steels have been found to have wide applications in hospitals and food indus- tries.In recent years epsilon copper precipitation in antibacterial stainless steels has obtained much research interest due to its antibacterial action.The objective of this study was to determine the effects of nitro- gen concentration on the precipitation of epsilon copper and antibacterial property.Two kinds of austenite antibacterial stainless steels containing copper and different nitrogen concentration(0.02 and 0.08 wt pct,re- spectively)were prepared and the microstructures were characterized by a combination of electron microscopy and thermodynamic analysis.A mathematical expression was deduced to predict the effect of nitrogen con- centration on the activity coefficient of copper,In(f_(Cu)/f_(cu)~0=0.53524+4.11x_N-0.48x_N~2.Higher nitrogen was found to increase the free energy difference of copper concentration distribution between precipitation phase and austenite matrix,stimulate the aggregation of copper atoms from austenite,increase the precipitation amount and consequently enhance the antibacterial property of steel. Austenite antibacterial stainless steels have been found to have wide applications in hospitals and food indus- tries. In recent years epsilon copper precipitation in antibacterial stainless steels has resulted in much research interest due to its antibacterial action. The Objective of this study was to determine the effects of nitro-gen concentration on the precipitation of epsilon copper and antibacterial property. Two kinds of austenite antibacterial stainless steels containing copper and different nitrogen concentrations (0.02 and 0.08 wt pct, re- spectively) were prepared and the microstructures were characterized by a combination of electron microscopy and thermodynamic analysis. A mathematical expression was deduced to predict the effect of nitrogen con- centration on the activity coefficient of copper, In (f_ (Cu) / f_ (cu) ~0 = 0.53524 + 4.11x_N- 0.48x_N ~ 2 .Higher nitrogen was found to increase the free energy difference of copper concentration distribution between precipitation phase and austenite matrix, stimulate the aggregation of copper atoms from austenite, increase the precipitation amount and more enhance the antibacterial property of steel.