The formation of core-shell structure is the key issue of temperature stable barium titanate-based dielectric ceramic for multilayer ceramic capacitor application. It is difficult to obtain and observe the core-shell structure in ceramic grains when the grain size becomes smaller, especially to sizes <200 nm. A nanodopant method has been developed for the preparation of ultrafine-grained barium titanate-based ceramics with grain size below 200 nm. The existence of core-shell structure was proved by transmission electron microscopy observation and energy-dispersive spectroscopy analysis. High-performance X7R dielectric ceramics were produced in a reducing atmosphere by normal sintering and two-step sintering method. The dielectric constant at room temperature could reach over 2000, with a low dielectric loss at about 1.0% and high insulation resistivity ∼1012Ω·cm.