[en] Brittle ceramics can be toughened by incorporating metallic inclusions. In the present study, the principles for the preparation of dense metal-toughened ceramic are proposed. The relationships between the microstructure and the properties of the composites are investigated. The mechanical properties of the composites are emphasized. Due to the wetting of most metallic melt on ceramics is poor, the amount of metallic inclusions can be added into ceramics is limited. Furthermore, the size of metallic inclusions has to be in range of one μm in order to achieve high density. To reduce the size of metallic inclusions, ceramic particles instead of metallic particles are added into the ceramic matrix. The ceramic particles are then sintered in a reducing atmosphere. Through suitable processing control, the size of the resulting metallic inclusions can be reduced to around 100 nm. Both the strength and toughness of the ceramic matrix are enhanced by adding metallic inclusions. The toughness enhancement is mainly contributed by plastic deformation of metallic phase. The strengthening effect is attributed to microstructural refinement. Examples on Al₂O₃/Ag, Al₂O₃/Ni, Al₂O₃/NiAl are reported. (author)