Alumina/SiC “nanocomposites" consist of a dispersion of submicron SiCparticles in an alumina matrix. The resistance to severe wear of thenanocomposites and the surface finish produced by a given grinding treatmentare strikingly superior to those of pure alumina with the same grain size.We have explored the reasons for this by correlating a wide range ofvariations in the basic microstructure with the wear behaviour observed,including both the wear rate, and quantitative surface fractography of theworn surfaces. These improved properties of the nanocomposites are shown tobe a consequence of a reduction in surface grain pullout by brittlefracture. In “dilute” nanocomposites (<10% SiC), this is due largely to areduction in size of the individual pullouts. With 10% SiC nanoparticles,however, there is also evidence that the SiC directly suppresses thenucleation of cracking by plastic deformation of the surface. The origin ofthese effects will be discussed.