The temperature dependence of dielectric constant was investigated for (Ba0.90Ca0.10)(1-2x)(Na0.5Bi0.5)(2x)TiO3 (BCT-NBT5 (x = 0.05), BCT-NBT15 (x = 0.15)) and (Ba0.90Ca0.10)(0.925)Bi0.05TiO3 (BCT-BiT5) ceramic samples prepared using the solid-state reaction technique. The dielectric relaxation behavior was observed in BCT-NBT15 and BCT-BiT5. The different dielectric relaxation mechanisms have been discussed for these two samples. in view of the defect chemistry, Raman spectroscopy was made on BCT-NBT5, BCT-NBT15, BCT-BiT5 and (Ba0.925Bi0.05)(Ti0.90Ca0.10)O-3 (BTC-BiT5). The development of the new Raman bands at 827 and 825 cm(-1) for BTC-BiT5 and BCT-BiT5, respectively, indicated that Ca2+ ions substitution for B-site Ti4+ ions has happened in BCT-BiT5 ceramics, giving the evidence for the formation of O2- vacancies. Raman spectroscopy and the temperature dependence of dielectric studies suggest that the dielectric relaxor behavior of Bi doped barium calcium titanate ceramics is related with the Bi3+ ions and the Ca2+ ions. (C) 2009 Elsevier B.V. All rights reserved.