Abstract: The friction and wear of rod-like mullite dispersed yttria stabilized tetragonal zirconia polycrystals (MDZ) sliding against a high-chromium cast iron in 5%NaOH solution containing 2wt%SiO_2 as the abrasive particles was investigated on an MM-200 test rig in a block-on-ring configuration. The worn surface morphologies were observed on a scanning electron microscope, and the effect of the sliding on the tetragonal-to-monolithic phase transformation of ZrO_2 and on the wear resistance of the composite ceramics was discussed, based on analyses of the original surface and worn surface of the composite ceramics by means of energy dispersive spectrometry and X-ray diffraction. It was found that the Y-TZP incorporated with mullite had better wear resistance than the one without the mullite dispersive phase, though the inclusion of the mullite led to damage to the mechanical strengths of the composite ceramics. The improvement in the wear resistance of the composite ceramics by the inclusion of the mullite was mainly attributed to the actions of the rod-like mullite particulates to restrain the crack propagation and grain boundary slippage, and to densify the ceramics as well. The MDZ ceramics was characterized by scuffing and plastic deformation as they slid against the cast iron at a relatively larger load, while the Y-TZP was dominated by plastic deformation and fracture under the same test conditions.