The structure-property relationship of the CaCu3Ti4O12 ceramics processed via conventional solid-state method was studied in terms of the different processing conditions. X-ray diffraction patterns of the tenorite CuO and cuprite Cu2O secondary phases found on the unpolished and polished surfaces of CaCu3Ti4O12 were explained by the reduction/reoxidation reaction as a function of sintering time. Based on the microstructures, grain growth of CaCu3Ti4O12 continued from 0.5 to 4 h sintering while the further growth was limited to the small-sized grains after 8 h sintering. Also, WDS data indicated the Cu-deficient and Ti-excessive stoichiometry of CaCu3Ti4O12 on both outer and inner regions regardless of sintering time. The change of dielectric constant and tan delta were shortly discussed with regard to the secondary phases and the microstructures of the different sintering hours.