Abstract—A new technological procedure for preparation of dense ceramics based on aluminum oxide is developed. It features use of a modifying additive and mechanochemical (MCA) activation of the starting material. Use of MCA has a beneficial effect on synthesis of dispersed precursor γ-Al2O3-based powders at 600°C, with the temperature of α-Al2O3 phase formation being reduced from 1200 to 1000°C. MCA is found to affect the relative density of aluminum oxide ceramics sintered at temperatures of 1000–1500°C, the sintering process occurring more intensely in the temperature range of 1000–1300°C. The presence of MgO in the aluminum oxide matrix at a level of 1 to 3 wt % is shown to slow down the growth of α-Al2O3 phase grains owing to the formation of a boundary layer consisting of MgAl2O4 nanocrystallites in the aluminum oxide matrix. A ceramic material prepared on the basis of α-Al2O3 has a mean grain size of ~70 nm, a relative density of 0.98, a microhardness of 25 GPa, and a bending strength of 650 MPa. The proposed combined method is facile and economical and enables us to produce high-density aluminum oxide ceramic with a grain size below 100 nm and high physicochemical characteristics. This ceramic can be used in fabrication of different construction and functional materials.