Abstract <p>The effect of the initial size of alumina particles on the density, microstructure, hardness, and fracture toughness of ceramics obtained by conventional and spark plasma sintering (SPS) has been studied. We studied ceramics obtained from commercial Al₂O₃ powders with an initial particle size of 40 to 50 nm, 0.2 μm, and 1 μm and domestic fine powders with an initial particle size of 0.2 to 3 mm, and Al₂O₃ + 0.25 vol % MgO and Al₂O₃ + 10 vol % ZrO₂. It is shown that the density of alumina ceramics nonmonotonically depends on the initial size of Al₂O₃ powder particles. It has been established that an increase in the grain size leads to a nonmonotonic change in the hardness of alumina ceramics. It has been established that the addition of 0.25 vol % MgO accelerates the sintering of alumina. The addition of 10 vol % ZrO₂ makes it possible to provide an optimal combination of hardness and fracture toughness. It is shown that fine-grained ceramics obtained by the SPS method have a higher hardness. It has been suggested that SPS of submicron alumina powders with an amorphous layer on the surface, additionally stabilized by zirconia particles, is promising for further increasing the hardness of alumina ceramics.</p>