In order to study the effect of copper ion implantation on the antibacterial property of AISI 420 stainless steel (SS), specimens were implanted by copper ions in a dose ranging from 2 x 10(16) to 5.0 x 10(17) ions cm(-2), using metal vapor vacuum arc source at an extracting voltage of 50 kV The microstructure, phase compositions and Cu ions concentration profile in the implanted layer were revealed by glancing angle X-ray diffraction, transmission electronic microscopy (TEM) and Auger electronic spectroscopy, respectively. Film attachment method was adopted for evaluation of antibacterial property of specimens against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). With TEM, changes of bacterial appearance on the surface of un-implanted SS and annealed Cu-implanted SS were observed separately. Results showed that novel phases such as Fe4Cu3 and Cu9.9Fe0.1 were formed in the surface layer of the annealed Cu-implanted SS and that the antibacterial property resulted from the Cu-contained and Cu-rich phase which had a damaging effect on pericellular membrane and cell wall. Furthermore, the pericellular membrane was thickened and then the karyon was degraded, and finally, bacteria died. Annealed Cu-implanted SS not only obtains excellent antibacterial property, but also keeps good corrosion resistance which is equivalent to that of common AISI 420 SS. (c) 2005 Elsevier B.V. All rights reserved.