Heavily deformed Cu-based composites attain anomalous increases in strength upon mechanical deformation. The unique filamentary micro-structures that evolve during processing (cold rolling, wire drawing or swaging) are the source of the strengthening. Composite strength is correlated to microstructural characteristics for arc melted Cu-20 vol.% Nb cold rolled up to a true strain of 6.9. During rolling Nb elongates and becomes ribbon-like while the Cu matrix undergoes a cycle of deformation-dynamic recovery-recrystallization which allows for the further reduction of the Nb. Longitudinal and transverse specimens have equivalent mechanical properties. The ultimate tensile strength of the sheet showed a weak dependence on Nb filament spacing and its strength is controlled by a dislocation propagation mechanism. TEM analysis of the composite sheet substructure revealed dislocation densities of 1-2 x 10[superscript]10/cm[superscript]2. TEM sample preparation of Cu by ion-thinning was found to increase the dislocation density of annealed Cu by more than 400% but had a relatively small effect on heavily worked Cu. The orientations and textures of Cu and Nb in the composite are evaluated by TEM;The feasibility of producing heavily deformed Cu-based composites via powder metallurgical processing techniques is explored because of the wider range of composite compositions which can be produced in contrast with ingot metallurgy. Specifically the mechanical and microstructural characteristics of hot extruded elemental Cu and Nb powders and Cu-Nb powders pre-alloyed by the rotating electrode process are examined.