Several zirconia-mullite and alumina-zirconia composites were prepared and their physical, chemical, mechanical and thermal properties determined. The phase assemblage, size of ZrO 2 crystals and microstructure of the composites were ascertained. This paper embodies a comparison of the alumina-zirconia and zirconia-mullite composites with respect to their properties and also the constitution-property relationships between each group of composites. Alumina-zirconia composites (AZ) were found to be superior to zirconia-mullite composites (prepared through ZMS or ZMC route) in almost all respects. Thermal-shock resistance and hydration resistance of the clay-based zirconia-mullite (ZMC) composites and alumina-zirconia (AZ) composites were almost at par.