NiAl-Al2O3 intermetallics based composite coatings were prepared by cold spraying of Ni/Al-Al2O3 composite powders followed by post-spraying annealing treatment. The phase transformation mechanism from Ni/Al mechanical alloy to intermetallics was explored to aim at controlling the microstructure of the composite coating. Results showed that, with the porous Ni/Al and Ni/Al-Al2O3 green compacts, self-propagating high-temperature synthesis (SHS) reaction was ignited at a temperature of 500-600°C. However, SHS reaction was not able to be ignited for the cold-sprayed dense Ni/Al alloy coating with or without substrate. SHS reaction was even not ignited for the Ni/Al-40vol.%Al2O3 composite coating, although the thermal conductivity of the coating was significantly decreased by the addition of Al2O3 ceramic particles. The phase transformation from Ni/Al mechanical alloy to NiAl intermetallics during post-spraying annealing can be evidently attributed to diffusion mechanism.