Thermally stimulated depolarization current (TSDC) measurements were performed on 3 mol% and 8 mol% yttria stabilized zirconia ceramics (3YSZ and 8YSZ), in order to observe defect associations. Several TSDC peaks were observed, and the characteristics suggested that the peaks were attributed to space charge polarization due to long range migration of oxygen vacancies and electric dipole polarization due to trimeric defect association of Y at Zr site (Y-Zr') and oxygen vacancy (Vo). The activation energies for the dipole polarizations were different between 3YSZ and SYSZ. The difference was caused by the difference of the structure of defect association. In addition, in 3YSZ, peaks with high activation energy of 124 eV were observed. The high activation energy suggests the presence of oxygen migration across Y-Y edges, in other word, indicating that Y-Y pairs exist in 3YSZ (C) 2014 Elsevier B.V. All rights reserved.