Microstructure and control of pore formation in SPS-synthesized alumina were investigated by TEM and SEM observation. In addition, the relationship between the morphology of pores in the alumina and the bending strength of the alumina was examined. SPS consolidation at a high heating rate of 200 °C/min and at a high pressure of 100 MPa is effective for the fabrication of nano-structured and highly-transparent alumina without residual pores. It has been indicated that the interrelation between plastic deformation, neck formation, heating rate, densification and grain growth is important for the synthesis of nano-structured ceramics without residual pores.