Six kinds of silicon nitrides with different microstructures were fabricated by changing the amount of sintering additives, Al2O3 and Y2O3. The hardness decreased with an increase in the amount of additives, whereas the indentation fracture resistance increased in the samples with large amount of additives due to the formation of coarse and elongated grains. The wear property of various Si3N4 ceramics was investigated in the sliding contact test without lubricant and was compared with the mechanical properties. The specific wear rate varied notably from 4x10-4 to 6x10-6 mm-3N-1m-1 depending on the compositions, which was difficult to explain directly from the hardness and fracture resistance. An indentation fracture model for material removal could correlate the wear properties with a function of hardness and fracture resistance of the materials, suggesting that the indentation model was likely to be valid for analyzing the wear behavior in this study.