The effects of ZrO2-3 mol % Y2O3 additives containing 7.3, 15, 23.3 and 32 vol % of ZrO2 on sigma(f), K(lc), H(v) and the microstructure of hot-pressed alumina-based ceramics were investigated. The presence of the m-, t- and t’-ZrO2 phases was discovered by using X-ray diffraction and transmission electron microscopy. An inhomogeneous distribution of Y2O3 in the ZrO2 grains was observed. The variation of the mechanical properties of the ceramics is explained by the influence of different toughening mechanisms and by a change in the structure of the material.