The properties of undoped and La-doped CaCu3Ti4O12 ceramics synthesized via solid state reaction under argon environment had been studied. It was found that La-doped CCTOs gave higher dielectric constant and lower dielectric loss than undoped CCTO. X-ray diffraction (XRD) analysis indicated that all of the sintered samples have single-phase cubic structure (space group ). A minor shifted was observed in the peak positions for La-doped samples, which are attributed to the lattice expansion. The lattice parameter obtained from XRD analysis is 7.348 Å for undoped CCTO and increases to 7.348 – 7.377 Å for La-doped CCTOs. The results proven that La ions have effectively substituted into the Ca site of CCTO.