AISI 304 stainless steel was ion implanted with Co, and the tribological property on the surface of the stainless steelwas investigated. The Co ion implantation was carried out using a metal vapor vacuum arc (Mevva) broad-beam ionsource with an extraction voltage of 40 kV, implantation doses of 3×10~(17)/cm~2 and 5×10~(17)/cm~2, and ion currentdensities of 13, 22 and 32μA/cm~2. The results showed that the near-surface hardness of Co-implanted stainless steelsample was increased by 50% or more, and it increased with increasing ion current density at first and then declined.The friction coefficient decreased from 0.74 to 0.20 after Co implantation. The wear rate after Co implantationreduced by 25% or more as compared to the unimplanted sample. The wear rate initially decreased with increasingion current density and then an increase was observed. Within the range of experimental parameters, there existsa critical ion current density for the Co-implanted stainless steel, at which the wear rate decreased AISI 304 stainless steel was implanted with Co, and the tribological property on the surface of the stainless steel was investigated. The Co ion implantation was carried out using a metal vapor vacuum arc (Mevva) broad-beam ionsource with an extraction voltage of 40 kV , implantation doses of 3 × 10 17 / cm 2 and 5 × 10 17 / cm 2, and ion current densities of 13, 22 and 32 μA / cm 2. The results showed that the near-surface hardness of Co-implanted stainless steels was increased by 50% or more, and it increased with increasing ion current density at first and then declined. The friction coefficient decreased from 0.74 to 0.20 after Co implantation. or more as compared to the unimplanted sample. The wear rate initially decreased with increasingion current density and then an increase was observed. Within the range of experimental parameters, there existsa critical ion current density for the Co-implanted stainless steel, at which the we ar rate decreased