In this report, effect of MgO and Y2O3 additives on modifying the dielectric constant-temperature (K-T curve) properties of the BaTiO3 materials for multilayer ceramic capacitors (MLCC), using base metals (Cu and Ni) as electrode materials was systematically studied. Low temperature coefficient of capacitance (TCC), which meets X7R specification, has been obtained. Microstructural examinations using transmission electron microscopy (TEM) indicate that small TCC of thus obtained materials is attributed to microstructural control of materials. Simulation using simplified microstructure model indicates that the effective dielectric constant of core-shell structured materials significantly not only with the dielectric properties of cores and shells, but also with the shell-to-core thickness ratio, which results in a K-T behavior extremely sensitive with the processing parameters. In contrast, the X7R type K-T properties for BaTiO3 materials can be obtained in a much wider processing window by forming duplexed structure. Simulation also indicated that the effective dielectric constant of such a duplexed material is relatively insensitive to the fluctuation of K-T properties of each component.