The elastic modulus of fluorite-structured pure ceria, gadolinium doped ceria (GDC) and yttria stabilized zirconia (YSZ) with different levels of oxygen vacancy concentration were measured by the nanoindentation technique. The samples were heat treated at 800 degrees C under an oxygen partial pressure in the range of 0.21 to 10(-25) atm for 15 h until equilibrium was reached at a sufficient depth. The defect concentrations were conserved to room temperature by fast cooling. The results reveal that the elastic modulus of both pure ceria and GDC decreases drastically in samples heat treated at very low partial pressures of oxygen. However, the elastic modulus change for YSZ, within the studied range, is insignificant. An analysis of the experimental results suggests that an increase in the point defect content weakens the attractive forces between atoms in fluorite-structured oxides. (c) 2006 Elsevier B.V All rights reserved.