Ceramic-based nanocomposites with intra-type nano-structure have high strength with moderate fracture toughness. In this research, the toughening and strengthening mechanisms of the ceramic-based nanocomposites will be explained by dislocation activities even in brittle materials. Based on these mechanisms, we fabricated toughened and strengthened alumina-nickel nanocomposites. Fracture toughness of the annealed nanocomposites was 7.6 MPam
, which was two times higher than that of monolithic alumina.