Gelcasting is conventionally used to acquire high-density ceramic parts; however, in this work, alumina (Al2O3) ceramics with ultra-low density (8%-40% theoretical density) were successfully fabricated by this method. In this research, polymerization of acrylamide was realized in tert-butyl alcohol/Al2O3 slurries with solid loading ranging from 5 to 15 vol%. Green bodies with ultra-low density could be dried with very small shrinkage, and relatively high green strengths (1-3 MPa) were achieved. By choosing different initial solid loadings and sintering temperatures, ceramic microstructures could be effectively controlled, with the porosity ranging from 60% to 92% and pore sizes from 0.1 to 2.2 mu m. Sintered Al2O3 showed high open porosity (90%), high specific area (14 m(2)/g) and high compression strength (> 10 MPa), which was attributed to the connection of Al2O3 particles. This technique is considered potentially useful in many applications, and introduces a new application field of gelcasting.