Although Ni-Al intermetallics are of excellent corrosion and oxidation resistance; their oxidation during thermal spraying limits the applications as thermal spray coating. Thus; controlling the oxidation is a necessary approach to improve their performances as the coatings. In this study; a novel approach is proposed to exclude oxide of in-flight Ni-Al droplets by introducing diamond as a deoxidizer in Ni/Al powder during plasma spraying. Ni-Al coatings were deposited with Ni/Al/diamond composite powder prepared by mechanical alloying by atmospheric plasma spraying at different spray conditions to study the effect of the diamond addition on the oxidation behavior of in-flight droplets. The phase composition; microstructure; porosity and microhardness of the coatings were characterized by X-ray diffraction; scanning electron microscopy; image analyzing and hardness test; respectively. The oxygen content of the coatings was measured quantitatively. The results show that APS Ni-Al coating prepared by Ni/Al/diamond powder presents significantly lower oxygen content. The measurement yields particle temperatures higher than 2300 °C. The low oxygen content in the coating is attributed to the in-situ deoxidizing effect of ultra-high temperature contained droplets. Moreover; the oxide-free droplets promote the deposition of Ni-Al coatings with lower oxygen content and porosity than the conventional Ni-Al coatings.