Ba0.68Sr0.32TiO3 ceramics of perovskite structure are prepared by solid state reaction method with addition of x mol% Sm2O3, and their dielectric properties are investigated. It is found that, integrating with the lattice parameters and tolerance factor t, there is an alternation of substitution preference of Sm3+ for the host cations in perovskite lattice. Owing to the replacement of Sm3+ ions for Ba2+ ions in the A site, T-c rises with the increase of Sm2O3 doping when the doping content is below 0.1 mol%; meanwhile, when the content is more than 0.1 mol%, Sm3+ ions tend to occupy the B-site, causing a drop off, Owing to the modifications of Sm3+ doping. dielectric constant, dissipation factor and temperature stability of dissipation factor are influenced remarkably, making it a superior candidate for environment-friendly applications. Moreover, the creation of oxygen vacancies controls the dielectric constant when the addition is above 0.1 mol%, so the dielectric constant decreases with increasing of samarium. (C) 2008 Elsevier Ltd. All rights reserved.