Nano-scaled nickel particles have attracted interest for its potential use as a fuel in energetic materials. In this work, we combined two ion-mobility spectrometry approaches; tandem differential mobility analysis (TDMA) and tandem differential mobility – particle mass analysis (DMA-APM) to study the size resolved reactivity of nickel nanoparticles. Nickel nanoparticles were generated in-situ using gas-phase thermal pyrolysis of nickel carbonyl. Four particle sizes (40, 62, 81 and 96 nm, mobility size) were then selected by using a differential mobility analyzer. These particles were sequentially oxidized in a flow reactor at various temperatures (25-1100 °C). The size and mass change of the size selected and reacted particles were then measured by a second DMA, or an APM. We found that both particle size and mass were increased as the temperature increased. However, at higher temperature (600-1100°C), a different mass and size change behavior was observed which could attribute to a phase transition between NiO and Ni2O3. A shrinking core model employed to extract the size- resolved kinetic parameters shows that the activation energy for oxidation decreased with decreasing particle size The burning time power dependence on particle size was found to be less than 2 and nickel particles were found to be kinetically more active than aluminum.