A series of Bi2/3Cu3Ti4O12 (BCTO) ceramics were prepared via conventional solid-state reaction underdifferent sintering temperature conditions. Their microstructures, crystalline structures and dielectricand electrical properties were investigated. It has been found that all of the BCTO ceramics show giantdielectric-permittivity values with low frequency ε_ larger than 1.5×105 at room temperature. Thereexist two relaxations in the dielectric dispersion spectra and three semicircles in the complex impedanceplane. In general, BCTO ceramics are qualitatively quite similar to CaCu3Ti4O12 (CCTO) ceramics in theaspect of dielectric and electrical properties. However, unlike CCTO ceramics, BCTO ceramics possessthe dense microstructures of small and uniformly distributed grains, which are insensitive to sinteringtemperature conditions. From analysis, we attribute the dielectric relaxation in the high frequency regionto an internal barrier layer capacitance (IBLC) effect associated with insulating grain boundaries andsemiconducting grains and the other one in the low frequency region to an electrode polarization effectdue to the Schottky barriers formed at electrode–ceramic interfaces.