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