Abstract: ZrO₂/A1₂O₃ composite ceramics were made by microwave sintering method.The influences of nano-ZrO₂ on the sintering,mechanical properties and microstructure of A1₂O₃ ceramics were discussed.The results show that the addition of ZrO₂ will affect the microstructure of A1₂O₃ ceramics,ZrO₂ particles coexist in intragranular and grain boundary,the phase of ZrO₂ are related to its content.A rational experimental prescription and preparation technology are propitious to ZrO₂ coexisting t-ZrO₂.When the content of ZrO₂ is 15vol%,ZrO₂ all exist in the form of t-ZrO₂,in favor of the stress induced phase transformation,its hardness,fracture toughness and flexural strength are 13350MPa,6.41MPa·m1/2 and 502MPa.ZrO₂/A1₂O₃ composite ceramics are toughened mainly by the stress induced phase transformation,Microcrack and the intragranular formation of zircoina.