Co/alpha-Al2O3 powder mixtures (5,10,20,30,40, and 50 mass % of alpha-Al2O3) have been ball-milled and, subsequently, consolidated at room temperature by means of a high pressure torsion procedure in order to produce bulk nanostructured composites. For mixtures up to 20% of alpha-Al2O3, the cold-compaction results in roughly fully dense disks with relatively high microhardness values. However, the compaction for 30, 40, and 50% of alpha-Al2O3 is less effective, resulting in a reduction of the microhardness although a structure in the nanoscale range is still preserved. A detailed structural investigation has been also performed.