Yttria-partially stabilised zirconia (Y-TZP) of 3 mol-% with 5.4, 10.5 and 19.9 vol.-% 64S bioglass compacts was sintered at 1300-1500°C. The influence of 64S content and sintering temperature on the mechanical properties and aging behaviour of Y-TZP ceramics were studied. Among Y-TZP ceramics with 64S additions, maximum hardness and flexural strength values were found for Y-TZP with 10.5 vol.-% 64S at 1400°C. Y-TZP with 19.9 vol.-% 64S at 1500°C presented the highest fracture toughness; crack deflection and pinning by ZrSiO 4 particles combined with zirconia microcracking contributed to the fracture toughness. Y-TZP at 1500°C was extremely susceptible to hydrothermal degradation and its flexural strength markedly decreased after aging. On the contrary, Y-TZP with 10.5 vol.-% 64S at 1400°C remained almost unaltered; it maintained its flexural strength at a high level during aging, becoming the most promising ceramic in terms of mechanical properties and aging behaviour.