Nanoenergetic composites are being examined for their use as energy storage and delivery materials. For this application, non-gas-generating mixtures that produce enough energy to sustain reaction propagation are ideal. A potentially promising formulation for this application is comprised of manganese (Mn) powder mixed with manganese dioxide (MnO2) because thermoequilibrium calculations predict that the Mn/MnO2 reaction is non-gas-generating and highly exothermic. The objectives of this study were to examine the flame propagation behavior of various mass percentages of Mn and MnO2 and evaluate the influence of fuel particle size. Results showed that conduction is the dominant energy-transfer mechanism for the reaction even in the loose powder configuration, regardless of the fuel particle size. Combustion wave speed (CWS) was measured as a function of the composition and Mn particle diameter. Nanometric Mn particles (referred to as nano-Mn) produced higher CWS than micrometric Mn particles (referred to as micro-Mn) for all of the mass percentages of Mn studied. This behavior was attributed to the manganese(II,III) oxide (Mn3O4) passivating shell around Mn particles, which created an oxygen-rich environment for the reaction zone. This finding is in contrast to nanometric aluminum (Al) particle (referred to as nano-Al) combustion studies, in which energy transfer is dominated by conduction (i.e., highly consolidated nanocomposite). For nano-Al, the alumina (Al 2O3) passivation shell does not participate in the oxidation reaction and, instead, acts to retard energy propagation as a heat sink. As a result, reducing the particle size of Al produces lower CWS. The CWS was found to be at a maximum of 12.01 mm/s for the nano-Mn/MnO2 reaction at a Mn mass percentage of 29%. Flammability limits are also defined.