The Young's modulus and the hardness of single crystals and polycrystalline sintered compacts of yttria-stabilized zirconia (YSZ), (Y2O 3)x(ZrO2)1-x (x = 0.08, 0.10) was investigated by using the nano-indentation method. Together with results obtained by the secondary electron microscope observation and the electron backscattering diffraction analysis, the effect of the crystal orientation on the mechanical properties was discussed. It was empirically demonstrated that the Young's modulus of YSZ depends on the crystal orientation. The Young's modulus of YSZ showed the highest value on the (001) surface while the lowest value on the (111) surface. However, the observed anisotropy of the Young's modulus was rather small compared with predicted one from the single crystal elastic constants in literature. Compared with the Young's modulus, the anisotropy of the hardness of YSZ was less significant.