Transparent ALON ceramics with the ultra-fine -ALON spinel powder were prepared by hot-pressing. The powder was prepared by carbothermal reduction method. The optimum condition was hot-pressing between 1850°C to 1920°C for 3 ~ 5 h under 35 MPa. We got transparent samples 70 × 3 mm with in-line transmittance above 70% in the range from the visible to infrared wavelength. The effect of additive contents on transparency and the relation of microstructure and transparency have been discussed in this paper. The transmittance is good when the Y2O3 sintering additive content is 1.5wt%. The sample density is about 99% of its theoretical density. We also measured the flexural strength, elastic modulus and other mechanical properties of ALON.