The effect of mechanical and field activation on the synthesis of dense nanometric MoSi2 was investigated. Powders of Mo and Si, milled separately or comilled in a planetary ball mill, were reacted in a spark plasma synthesis (SPS) apparatus under different electric current conditions. Milled powders reacted faster and required less current than unmilled powders. Mixtures of powders which were milled separately (to nanometric size) reacted in the SPS to produce micrometric α–MoSi2. Similar results were obtained for samples comilled to produce nanometric reactants which did not contain detectable amounts of the product phase. When products form during milling, they contain both the α and β modifications of MoSi2. The product after the SPS reaction was nanometric MoSi2 with a crystallite size of 140 nm.