The pressureless sintering behavior of /Cu powder mixtures, prepared from /CuO and /Cu-nitrate, has been investigated. Microstructural observation revealed that powders with nano-sized Cu particles could be synthesized by hydrogen reduction method. The specimens, pressureless-sintered at for 4 min using infrared heating furnace with the heating rate of /min, showed the relative density of above 90%. Maximum hardness of 16.1 GPa was obtained in /MgO/Cu nanocomposites. The nanocomposites exhibited the enhanced fracture toughness of 4.3-5.7 , compared with monolithic . The mechanical properties were discussed in terms of microstructural characteristics