CaCu3Ti4O12 (CCTO) ceramics were sintered in air and in oxygen, and the oxygen pressures are 1 atm and 3 atm, respectively. The results of dc electrical conduction and dielectric measurement show that for the CCTO ceramics sintered in oxygen, leakage, grain conductivity and the low-frequency dielectric constant are greatly reduced; these changes of electrical properties may be attributed to the enhancement of activation energies for electrical conduction in grain. In addition, for the CCTO ceramics sintered in oxygen, in the spectra of dielectric loss the strong peaks appear in the low-frequency range, which may be attributed to the contact-electrode effect on ceramic surface. (c) 2012 Elsevier Ltd. All rights reserved.