In this paper, the dielectric relaxation process in 11 mol% yttria-stabilized zirconia (YSZ) crystals were studied by using thermally stimulated depolarization current (TSDC) method and the origin responsible for dielectric polarization was discussed. TSDC measurements were performed in the temperature range of 173-500 K. By fitting the measured data with theoretical TSDC curves of dipole polarization, four peaks, with the activation energy of 0.46 eV, 0.99 eV, 1.15 eV, and 2.10 eV respectively, were observed. The origin for the peaks was attributed to the different migration paths of oxygen vacancies.