Nanocrystalline copper powder and Cu-TiN blends were prepared via oxidation of micron/submicron Cu powders followed by attrition milling of the Cu oxide formed with or without TiN nanoparticles. This was followed by reduction of the oxide to Cu metal and cold sintering/high pressure consolidation in air or in vacuum, The materials obtained were further annealed at 200 to 800degreesC in order to study the thermal stability of microstructure. Microstructure characterization was performed by X-ray diffraction, scanning electron microscopy with energy dispersive analysis (SEM/EDS) and high resolution SEM (HRSEM). The microhardness and yield stress of as-consolidated and annealed nanoscale Cu-based materials were measured. The described processing route yielded near fully dense nanocrystalline copper and Cu-TiN nanocomposites. The mechanical properties of materials obtained were significantly higher than those of conventional Cu. based alloys. Annealing at > 400degreesC of Cu and Cu-TiN specimens cold sintered in air resulted in a decreased density and lower mechanical properties not accompanied by any noticeable growth of the nanograins. At the same time, no density or mechanical properties decrease was observed after similar anneals for specimens cold sintered in vacuum. The expansion of air-consolidated Cu-based materials is assumed to be due to the presence of entrapped air in the nanopores. Cu based nanocomposites can be used for high strength wear resistant electric contacts or for fabrication of bearings where combination of high hardness/strength with high thermal conductivity is important.