High strain rate superplastic forming is the key issue of the industrial application of superplastic ceramic and is also an effective approach to achieve “near-net shaping” of ceramic parts with complicated shape. The sol-gel method was adapted to synthesize the nano-sized composite powders. A three-phase nanocomposite ceramic Al2O3-30mol%YSZ-30mol%MgAl2O4 (AZ30S30) was prepared by using hot-pressing sintering in vacuum. Then the superplastic forming of a ceramic part with relatively complicated shape was accomplished and some new characters in superplastic forming were studied. The results demonstrate that as-sintered ceramic is a typical inter/intra granular nano-structured composite. Because the dispersed second phase inhibited the growth of the alumina matrix grains in deformation as well as in sintering, the material behaves excellent superplastic formability. The extrusion forming at a high strain rate was achieved and the part in cup shape was obtained. The yttrium element segregated obviously at the grain boundary after deformation, which demonstrated that the yttrium element directionally diffused during the deformation. The mechanical properties of the ceramic did not change much after extrusion. The maximum hardness of as-deformed composite ceramic is 32GPa, a litter lower than that of 35GPa before deformation.