Silicon nitride with various amount of AlN as a sintering aid was sintered by a hot press method. Densified silicon nitrides were obtained, and it was found that the mechanical and wear properties were dependent on the contents of AlN. The effect of CUP phase on the mechanical and wear properties of silicon nitride was investigated. The properties were changed depending on the amount of alpha/beta phase. In the brittle materials, tribological behaviors were dependent on the microstructure as well as hardness and fracture toughness. We focus on the relationship between the microstructure and mechanical/wear properties of silicon nitride including AlN additives.