Cubic spinel aluminum oxynitrideAluminum oxynitride (γ-AlON) stands out as a solid solution within the Al2O3-AlN binary phase system, known for its exceptional transparency from ultraviolet to mid-infrared regions, as well as its low density, high melting point, high hardness, and mechanical strength. However, high temperatures and long durations are required to obtain highly dense single-phase AlON structure via conventionalConventional sintering methods. Reactive spark plasma sinteringReactive Spark Plasma Sintering (R-SPS) is a time-energyEnergy efficient process, enabling the synthesis and densification of AlON in one step, in a shorter time and at lower temperatures than other methods. MgO is one of the mostly utilized sintering additive in order to promote densification and achieve good transparency in AlON ceramics. In this study, 0.5–1–1.5wt.% MgO added AlON ceramics were prepared by R-SPS by using α-Al2O3 and AlN as starting powders. The effects of MgO addition on phase composition, densification, microstructure, hardness, fracture toughness, and transparency were investigated.