In this study, the hardness, fracture toughness, and abrasive wear behavior of three zirconia-toughened MoSi 2 composites and a zirconia-toughened Al 2 O 3 were examined and compared with similar materials containing no zirconia second phases. Each of the composites contained 20 vol.% ZrO 2 ; however, the polymorph of the added zirconia particles was varied to give composites with unstabilized, partially stabilized, and fully stabilized zirconia reinforcement. It was observed that the influence of zirconia toughening on the abrasive wear behavior depended upon the nature of the toughening mechanisms activated by the zirconia addition.