The microstructures and dielectric properties of Y-Mg-Ga-Si co-doped barium titanate ceramics were investigated. Y3+ dissolved in the lattice of BaTiO3 replacing both Ba2+ site and Ti4+ site, and Mg2+ replaced Ti4+ site. The replacements of Y3+ and Mg2+ inhibit the grain growth, cause tetragonal-to-pseudocubic phase transition, reduce the dielectric loss, and flatten the temperature dependence of capacitance curve. The incorporation of Ga3+ can improve sintering and increase permittivity. Y3+ and Ga3+ tended to remain close to the grain boundaries, and play an important role as a shell maker in the formation of the core-shell structure in the co-doped BaTiO3 ceramics. Excellent dielectric properties: epsilon(r) = similar to 2487, tan delta = similar to 0.7% (at 1 kHz), Delta C/C-25 < similar to 6.56% (from -55 degrees C to 125 degrees C) and alternating current breakdown voltage E < similar to 4.02 kV/mm can be achieved in the BaTiO3-0.02Y(2)O(3)-0.03MgO-0.01Ga(2)O(3)-0.005SiO(2) ceramics sintered at 1380 degrees C. This material has a potential application in alternating current multilayer ceramic capacitor. (C) 2014 Elsevier Ltd. All rights reserved.