Abstract Pure and 0.8 at % Nb-doped BaTiO3 were sintered between 1175 and 1250°C. Structural, microstructural and electrical properties were determined. A. c. conductivity and electromechanical coefficients were measured in as-prepared samples and at different time intervals until a year after. In pure BaTiO3 the aging process increases the bulk and grain boundary resistivity. Samples, poled near the Curie temperature, showed an anomalous aging effect on kt. In Nb-doped samples, a decrease in the grain boundary resistivity was observed after one year aging. An exceptionally high thickness coupling factor of 0.62 was found in as-poled samples, which strongly decreased with time.