Stabilized ZrO2-Y2O3 ceramics have been prepared with varying grain sizes and microstructures with the help of different preparation techniques. Bi2O3 has been added as a sinter aid to some of the samples. This results in a certain amount of a zirconia-rich second phase. For Bi2O3-free samples the fracture toughness (K lc), and therefore the fracture energy, increases with decreasing grain size. A linear relation with the inverse square root of the average grain size is found. The highest value ofK lc amounts to 4.1 MPa m1/2. Fracture toughness values of 1.9±0.2 MPa m1/2 are measured for Bi2O3 containing materials. The fracture surfaces are intergrannular for Bi2O3-containing and transgranular for Bi2O3-free samples, respectively.