Spark plasma sintering (SPS) is adopted to fabricate transparent AlON ceramics at 1350–1500 °C under 40 MPa, using a bimodal γ-AlON powder synthesized by the carbothermal reduction and nitridation method. After holding 10 min, high density samples are obtained, and their optical transmittance is investigated over the wavelength range of 1330–6000 nm. Despite the samples SPS-processed at 1350 °C indicate the presence of three-phases: γ-AlON, α-Al2O3, and h-AlN, they show high infrared transparency, i.e., the maximum transmittance for 1.2 mm thick specimens is up to 77.3% at ∼3900 nm. Also, the processed samples exhibit high hardness of 17.81 GPa. The high infrared transmittance should be mainly attributed to high density and rationally controlled grain size distribution, and the high hardness is apparently caused by a small grain size.