Abstract: Cu/Nb composite wires in different diameters were obtained through plastic deformation. Load-displacement curves were tested during nano-indentation test on different regions of the Cu/Nb composite wires. The characteristic of the indents was observed by scanning electron microscopy (SEM) and scanning probe microscopy (SPM). The influence of test region on the hardness of the composite wires was investigated. The results show that the ratio of the final displacement after complete unloading to the displacement at peak load (hf/hmax) was smaller than 0.8, very little pile-up and smooth surface around the indents were found in the nano-composite region of Nb core, Cu-0 and Cu-1 layers. The hardness of this region reflected the hardness of Cu/Nb composite accurately. Moreover, the hardness of the composite increased with the diameter of Cu-Nb wire decreasing.