Two sets of (Mg,Y)-doped BaTiO₃ samples were prepared to investigate the effects of the core/shell volumetric ratio on the dielectric-temperature behavior of BaTiO₃: one set with samples of the same grain size but different core sizes and the other with samples of the same core size but different shell thicknesses. The microstructural variation of the samples was characterized and their dielectric properties were measured. For both sets of samples, the temperature stability of the dielectric properties was generally improved with a reduction of the volumetric shell ratio regardless of the grain and core sizes. There existed, however, a limit of the reduction; for the studied range, shell thickness of one third of the core radius appeared to be an optimum thickness for the given amounts of dopants. It was concluded that the volumetric shell ratio should be optimized so as not to exceed a specific limit, for our case two thirds of the grain volume, to secure temperature stability of the dielectric properties of BaTiO₃.