When ceramics are used as a slider material, both the wear resistance of ceramics themselves and no damage to the pair material are required. In high speed sliding, Y2O3-doped partially stabilized ZrO2 adheres to pair materials and protects them, but ZrO2 wears easily as compared with other ceramics. In this study, using Al2O3-ZrO2 composites, we investigated the optimum condition to improve the wear resistance of ZrO2 while protecting the pair materials. As results, in the combination with Si3N4, the optimum content of Al2O3 at which wear decreased to one-hundredths was detected. In this content, ZrO2 and Al2O3 grain dispersed excellently with the grain size in the order of 0.1μm. It was confirmed that the microstructure and density of ceramics affected the wear properties. Furthermore, to consider the mechanism of wear resistance, the sliding surface observed by SEM and optical microscopy. It was estimated that the sliding mechanism differed from that of Al2O3 and ZrO2 ceramics in the ZrO2-Al2O3 composites.