To study the effect of second sintering on intragranular structure and mechanical properties of 10vol%Al2O3/3Y-TZP composites, the composites were prepared by ball-milling nano-γ-Al2O3 and nano-ZrO2(3mol%Y2O3), pressing unidirectionally, cold-pressing isostatically, then first sintering at 1400°C for 2h and second sintering at 1600°C for 5h in air. The composition and microstructure of the composites were examined by X-ray diffractometer and scanning electron microscope, transmission electron microscope. The results showed that the second sintering changed the microstructure and fracture mode. After second sintering, the structure of fine grains was changed into the mixed one of large grains and small grains . Many large grains contained small grains, forming intragranular stucture that could be produced by the interblending of not only Al2O3 and ZrO2 but also ZrO2 itself. The intergranular fracture after first sintering was changed into transgranular fracture and intergranular fracture after second sintering . The second sintering led to grinds growing up and intragranular forming, which enhanced the contribution of the phase transformation toughening. Although the second sintering resulted in abnormal increase of grain size, the fracture strength and the fracture toughness of the composite were 667 MPa and 12.9 MPa⋅m1/2, respectively, due to the intragranular structure and the enhanced phase transformation toughening.