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Nd-doped BaTiO 3 ceramics with Ti vacancy compensation were prepared by a solid-state reaction method, and the lattice structures were identified by XRD and Raman spectra. Samples with light doping possess a tetragonal structure at room temperature, while the cubic phase appeared as the doping content increased. Dielectric properties at low temperature (−100–0 °C) were characterized by the dielectric constant, complex impedance and electric modulus. Colossal dielectric constant and dielectric relaxation processes appeared in all samples. Three electrical responses were observed in the low doping content ceramics, while four appeared in the high doping content ceramics by a combined plot of Z″ and M″. These responses were attributed to the microstructure inhomogeneity, which in turn can be ascribed to charge segregation when the doping content is high. Localization of charge carriers was also observed in all of the ceramics, and the confined carriers preferred to exist in the grain when the doping content was low, while localization would be more significant in grain boundaries with increased dopant. The localization could be ascribed to the formation of defect complexes, which on one hand maintained a high resistivity to the ceramics, and on the other hand, resulted in polarization of the dipoles. Both Maxwell-Wagner polarization and dipole polarization were found to exist in the Nd-doped BaTiO 3 ceramics and were responsible for the colossal dielectric constant and relaxations. The space charge, defect complexes, and microstructure are assumed to be responsible for the change in the dielectric constant and the relaxation mechanism. [ABSTRACT FROM AUTHOR]