The effect of the microstructure on the mechanical properties and the cutting performance of Al₂O₃-30wt%Ti(C, N) ceramics was studied. Three Al₂O₃-Ti(C, N) ceramics with average Al₂O₃ grain size of 1.6-1.9μm, 1.0-1.2μm and 0.7-1.0μm were obtained by presintering and HIPing. Large Ti(C, N) grains were mainly distributed at the grain boundaries and prevented the grain growth of Al₂O₃ grains. But in the ceramics with large Al₂O₃ grains, some fine Ti(C, N) particles were dispersed within Al₂O₃ grains. As microstructure became finer, the bending strength increased and the fracture toughness K_IC decreased. In the cutting test of tool steel (SKD11), the flank wear became less and the tool life became longer as the grain size decreased and N/(C+N) ratio in Al₂O₃-Ti(C, N) increased.