Two kinds of different structured alumina—titania composite powders were used to prepare alumina matrix ceramics by microwave sintering.One was powder mixture of alumina and titania at a micron—submicron level,in which fused-and-crushed alumina particles(micrometers) was clad with submicron-sized titania.The other was powder mixture of alumina and titania at nanometer—nanometer level,in which nano-sized alumina and nano-sized titania particles were homogeneously mixed by ball-milling and spray dried to prepare spherical alumina—titania composite powders.The effect of the microstructure of composite powders on microstructure and properties of microwave sintered alumina matrix ceramics were investigated.Nano-sized composite(NC) powder showed enhanced sintering behavior compared with micro-sized composite(MC) powders.The asprepared NC ceramic had much denser,finer and more homogenous microstructure than MC ceramic.The mechanical properties of NC ceramic were significantly higher than that of MC ceramic,e.g.the flexural strength,Vickers hardness and fracture toughness of NC ceramic were 85.3%,130.3%and 25.7%higher than that of MC ceramic,respectively.The improved mechanical properties of NC ceramic compared with that of MC ceramic were attributed to the enhanced densification and the finer and more homogeneous microstructure through the use of the nanostructured composite powders. Two kinds of different structured alumina-titania composite powders were used to prepare alumina matrix ceramics by microwave sintering. One was powder mixture of alumina and titania at a micron-submicron level, in which fused-and-crushed alumina particles (micrometers) was clad with submicron-sized titania. the other was powder mixture of alumina and titania at nanometer-nanometer level, in which nano-sized alumina and nano-sized titania particles were homogeneously mixed by ball-milling and spray dried to prepare spherical alumina-titania composite powders. The effect of the microstructure of composite powders on microstructure and properties of microwave sintered alumina matrix ceramics were investigated. Nano-sized composite (NC) powder showed enhanced sintering behavior compared with micro-sized composite (MC) powders. The asprepared NC ceramic had much denser, finer and more homogenous microstructure than MC ceramic. mechanical properties of NC ceramic were significantly higher t han that of MC ceramic, eg the flexural strength, Vickers hardness and fracture toughness of NC ceramic were 85.3%, 130.3% and 25.7% higher than that of MC ceramic, respectively. improved mechanical properties of NC ceramic compared with that of MC ceramic were attributed to the enhanced densification and the finer and more homogeneous microstructure through the use of the nanostructured composite powders.