Nano-sized powders of CaCu3Ti4O12 (crystallite size of 44, 58 and 71 nm) have been synthesized by a polymerized complex method, followed by calcination the synthesized precursor at 600, 700 and 800°C in air for 8h. The CaCu3Ti4O12 powders were then characterized by XRD, FTIR and SEM. Sintering of the powders was conducted in air at 1100°C for 16h. The XRD results confirmed a typical perovskite CaCu3Ti4O12 structure in all the sintered ceramics, although the presence of a second phase of CaTiO3 was observed in the sample sintered using the powders calcined at 600°C. Microstructure of the sintered CaCu3Ti4O12 ceramics was observed by SEM and the grain size of the materials evaluated with polished using the line intercept method were found to be ~ 10-20 μm. A giant frequency-dependent dielectric constant samples (ε ~10000-60000) with weakly temperature dependence and was observed in the all the samples. The highest dielectric constant of the material was found to be ~60000 (at 140-160°C, 100 Hz) in the sample sintered using the powders calcined at 700°C. The origin of the high permittivity observed in these CaCu3Ti4O12 ceramics is attributed to the Maxwell-Wagner polarization mechanism.