Sliding wear behavior of submicrometer-grained (grain size=0.45 mu m) alumina was investigated in air and distilled water and the result was compared with the wear characteristics of similar material with coarser grain sizes. Experiments were conducted with a pin-on-disk wear-testing machine under identical test conditions. Alumina with submicrometer grain size exhibits substantially higher wear resistance compared with the coarser-grained materials in both the environments. Scanning electron micrograph of the wornout samples revealed that in air, formation and subsequent degeneration of the compacted layer of wear-debris on the sliding surface govern the wear loss. In distilled water, no compacted layer was observed and in such cases, grain pullout through coalescence of microcracks along grain boundaries was found to be the dominant mechanism of wear.