Abstract The intrinsic defects of (Na 0.5K 0.5)NbO 3 (NKN) ceramics fabricated by high-energy ball-milling have been studied. In order to obtain the different amounts of Na/K evaporation, NKN ceramics were sintered in air (NKN exposed samples) and in calcined NKN powder (NKN buried samples), respectively. Compared with the dielectric and piezoelectric properties of the buried samples, the exposed samples exhibited a donor doped behavior at room temperature. A dielectric relaxation, induced by intrinsic oxygen vacancies, was detected in paraelectric phase region. The activity energies of intrinsic oxygen vacancies are 1.04 eV and 1.47 eV for the exposed samples and buried samples, respectively. The difference of activity energies resulted from singly ionized oxygen vacancies translating into doubly ionized oxygen vacancies with the increase of Na/K evaporation.