The relaxation dispersion of the bulk ionic conductivity of cubic zirconias stabilized with yttria, calcia and magnesia has been investigated between 450 and 1200 K at frequencies ranging from 20 Hz to 1.2 GHz. The relaxation process is attributed to the diffusional polarization due to the short-range oxygen vacancy jumping in the crystal lattice and allows one to determine the corresponding diffusion coefficients as well as the mobilities of oxygen vacancies. A good agreement was found between the activation energy of the ionic conductivity and the activation energy of the diffusion of charge carriers. The calculated concentration of mobile oxygen vacancies does not change with temperature and is equal to the concentration of all extrinsic oxygen vacancies created by doping.