This thesis investigates the effect of carbon nanotube (CNT) length (including the use of short multiwall CNTs) and the milling time on nickel powder crystallite size and dislocation density of mechanically milled Ni with 10 vol.% (4 wt.%) CNT (Ni-CNT) composite powder. Results illustrate that short CNTs interact differently during milling than the long CNTs resulting in more refined matrix microstructures, increased strain and dislocation densities within the milled Ni-CNT powders compared with longer CNTs. The Ni-CNT powders were also investigated as precursors in the electrically-activated reactive processing of nickel aluminide-CNT (Ni/Al-CNT) composites using a two-stage mechanical milling technique. Powders were re-examined following second stage milling with aluminum to determine the additional effects on the microstructure. Powder compacts were pressed and synthesized via electrically-activated reactive synthesis (EARS). Compacts with short CNTs resulted in better reaction characteristics producing composites with more Ni3Al content and greater hardness than reacted compacts with longer CNTs.