In this study, Ba4RCo0.5Nb9.5O30 (R = La, Nd, Sm, Eu) (BRCN) ceramics were synthesized using a high-temperature solid-state reaction. The effects of rare-earth ions with different ionic radii at A sites on the phase structure, microstructure, and dielectric properties of ceramics have been systematically studied. The full profile refinement XRD results show that all ceramic samples are tetragonal tungsten bronze