Nano-structured Si2N2O-Sialon composites were prepared by liquid phase sintering method with the amorphous nano-sized Si3N4 and nano-sized AlN powders. Nano-sized Al2O3 and Y2O3 powders synthesized by polyacrylamide gel method were introduced as additives. SEM examination shows the grain size of sintered body to be less than 80nm. Superplastic extrusion can be undertaken at 1550°C with a high velocity of 0.5mm/min and a big extrusion ratio of 3.57. There are a lot ring-shaped structure just like “annual ring” of trees in radial fracture and clear flow trace in axial fracture, all which is very similar to deformed metal materials and approve good superplastic deformation capability of Si2N2O-Sialon composites.