Porous gadolina-doped ceria (Ce0.9Gd0.1O1.95, GDC10) is commonly used as a functional electrode support in solid oxide fuel cells, gas sensors, and gas separators. In addition, dense GDC10 is commonly used as a solid oxide fuel cell electrolyte and a gas separation membrane. Although, porosity affects a wide range of electrical, thermal, and mechanical properties of solids, this study focuses on (i) the Vickers indentation hardness, H, as a function of volume fraction porosity, P, ranging from 0.08 to 0.60 and (ii) the load dependence of H for Vickers indentation loads of 0.98-9.8 N. For the 13 GDC10 included in this study, the decrease in H with increasing P is approximated by the empirical relationship H = H (0) exp(-b (H) P), where H (0) = 5.844 GPa and b (H) = 6.68. In addition, the H values were roughly independent of the applied load.