AlN ceramics were prepared by hot-pressing process with Y(NO3)3·6H2O as a sintering additive. Microstructure and mechanical properties of sintered AlN ceramics were measured and compared with that of monolithic AlN ceramic prepared by the same process. The results showed that the density and mechanical properties of monolithic AlN ceramics were drastically enhanced by adding Y(NO3)3·6H2O. Especially, the AlN ceramic with 3.24 wt% Y(NO3)3·6H2O (2 wt% Y2O3) displayed striking enhancement in mechanical propertie. However, such enhancement did not follow a consistent behavior with the increase of Y(NO3)3·6H2O content. A significant drop present at contents over inflection point (3.24 wt% Y(NO3)3·6H2O).