Ceramics are used in applications requiring strength, hardness, light weight, and resistance to abrasion, erosion, and corrosion, at both ambient and elevated temperatures. However, traditional ceramic materials are characteristically brittle, and this brittleness limits their use. While reduction of brittleness has been obtained with fiber-reinforced ceramic matrix composites, there continues to be a need for materials that combine the desirable properties of ceramics with improved fracture toughness. The discovery of this invention is that ceramic nanocomposites comprising nanotube fillers and nanocrystalline ceramic materials display improved fracture toughness over monolithic ceramic materials. In particular, carbon nanotubes exhibit surprising stability as fillers in nanocrystalline ceramic oxide matrixes and produce significant improvements in fracture toughness in the final composite material.