Microstructure and texture evolution of as-drawn and annealed Cu-Nb microcomposite wires were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The variation of hardness of the wires with the annealing temperature was investigated using nanoindentation. The results show that the Nb fibers begin to spheroidize and the nanoscale Cu matrix to recrystallize when annealed at 400-500 ℃. The texture of wires changes insignificantly after annealing, maintaining a strong <111>_Cu//<110>_Nb fiber texture along the wire axis. Nanohardness was analyzed by the rule of mixtures and the confined layer slip (CLS) model, respectively. The nanohardness is fitted well with the CLS model before the spheroidization of the Nb fibers, while the nanohardness conforms to the rule of mixtures when the annealing temperature is above 800 ℃.