The effect of sintering time on chosen mechanical and tribological properties of silicon nitride (Si3N4) with 5 wt.% of yttrium aluminium garnet (Y3Al5O12) ceramics was investigated. Si3N4 ceramics sintered for shorter sintering time contained a larger portion of untransformed -Si3N4 phase which has higher hardness compared to tougher β-Si3N4 phase. The fracture toughness of Si3N4 ceramics increased with the prolongation of its sintering time. Microcutting wear mechanisms predominated during grinding of Si3N4 ceramics with Al2O3 abrasives. The hardness of ceramic material had a supreme effect on its wear resistance. The wear of ceramics at friction with 18Cr-8Ni type of austenitic stainless steels was several times higher compared to friction with 14Cr type of ferritic stainless steel. In these conditions, microcracking wear mechanisms predominated.