A study of the annealing of defects in CaHfO3produced by181Hf thermal neutron activation is presented. Two defect structures besides the undistorted lattice were detected. One of them characterized by well-defined hyperfine parameters disappears at 1243 K. The other one vanishing at 1343 K, is characterized by a very strong and unresolved hyperfine interaction. The temperature dependence of site-fractions follows an exponential lawe−δe/kT. The activation energies of 1.5 eV and 0.1163eV were obtained upon annealing those structures.