Yttrium-doped α-sialon ceramics with different compositions were prepared by two-steps hot pressing (first heating to 1750 °C holding for 60 min, then continue heating to 1900 °C holding for 60 min) at 25 MPa in nitrogen, their design compositions were Y0.4Si9.8Al2.2O1.0N15 (Y1210, m=1.2 and n=1.0), Y0.4Si9.7Al2.3O1.1N14.9 (Y1211, m=1.2 and n=1.1) and Y0.4Si9.6Al2.4O1.2N14.8 (Y1212, m=1.2 and n=1.2) respectively, and the effects of n value on phase composition, microstructure and optical property were approached. It is found that only α-sialon is detected in Y1210, however, there exist β-sialon besides of major phase α-sialon in Y1211 and Y1212. The density of sintered sample decreases with the increase of n value, higher n value contributes to elongated grain growth, and both the size and content of elongated grain increase with the increase of n value. The samples all show light transmission in the near infrared and infrared region, and their maximal optical transmittances decrease with the increase of n value. All those indicate that lower n value contribute to higher density, single α-sialon phase, smaller size and lower content of elongated grain, which is better for the preparation of higher optical transmittance Y-α-sialon.