The effects of the contents of ZrO 2 (3Y) and ZrO 2 (2Y) on the sintering densification, microstructure and transformation behavior of the composites Al 2 O 3 /ZrO 2 (Y 2 O 3 ) were analyzed, which was prepared by vacuum sintering. It was found that volume fraction of ZrO 2 (Y 2 O 3 ) affected the transformation amount of t→m-ZrO 2 . The results also show that when the contents of ZrO 2 (3Y) and ZrO 2 (2Y) were 15 and 20vol.%, respectively, the relative densities of the Al 2 O 3 /ZrO 2 (Y 2 O 3 ) composites were 99.6% and 99.1%, and the average grain sizes of ZrO 2 (Y 2 O 3 ) were 1.3 and 1.5μm, respectively. In addition, the transformation quantities of the samples before and after fracture were V t→m =44vol.% and V t→m =18vol.%.