Reactions in energetic Al-MoO3 nanocomposites prepared by arrested reactive milling were investigated by scanning calorimetry and heated filament ignition experiments. The calorimetry data were processed to obtain kinetic parameters describing the reaction between Al and MoO3. The reaction was treated as a combination of four sub-reactions, which were described by a combination of a diffusion-controlled reaction model and first-order reactions. The activation energies determined in this study allowed the comparison to reference values for the decomposition of MoO3 and the diffusion of oxygen through an Al2O3 product layer. The kinetic model was extrapolated to high heating rates in the 10 3-106 K/s range and compared to ignition data. It was concluded that ignition of Al-MoO3 nanocomposites prepared by arrested reactive milling is primarily controlled by oxygen diffusion in Al 2O3.