Large scale translucent yttrium-doped α-sialon (80 mm in diameter) with the composition of Y0.4Si9.6Al2.4O1.2N14.8 (m=1.2 and n=1.0) was prepared by two-steps hot pressing sintering (first heating to 1850 °C holding for 30 min, then continue heating to 1900 °C holding for 30 min) at 25 MPa in nitrogen, and the optical property was approached over the wavelength range 900-5000 nm. The results showed that dense sample was obtained and its assemblage only consisted of single α-sialon phase. The large scale sialon had uniform and higher infrared transmittance property. The maximum infrared transmittance for 1.0 mm thick specimen could reach 66% at 3200 nm. It is attributed to the dense, uniform, equaxed microstructure. In addition to high optical transmission property, the sample showed higher hardness of 20 GPa and better fracture toughness of 5 MPa•m1/2.