To meet the needs of future multilayer ceramic capacitors (MLCCs), thinner dielectric layers are necessary. To achieve this goal, the grain size and uniformity of the particles must be effectively controlled. In this study, we confirmed a core-shell particle structure by means of X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The dielectric properties of the ceramics were measured using an LCR meter. We found Ba0.991Bi0.006TiO3 particles form a core that was coated with a homogeneous Nb2O5-Co3O4 layer (similar to 9 nm). The relationship between core-shell structure and epsilon(r)-T curves of the Ba0.991Bi0.006TiO3@Nb2O5-Co3O4 ceramics by different sintering temperature has been investigated. Dense, fine-grained Ba0.991Bi0.006TiO@Nb2O5-Co3O4 ceramics were obtained by sintering at 1160 degrees C. The ceramics met the X8R requirements, with a maximum dielectric constant of 2795, and a low dielectric loss at room temperature of 0.89%.