(1−x)BaTiO3–xBi(Mg1/2Ti1/2)O3 [(1−x)BT–xBMT] polycrystalline ceramics were obtained via solid-state processing techniques. The solubility limit for (1−x)BT–xBMT was determined to be about x=0.07. A systematic structural change from the ferroelectric tetragonal phase to pseudocubic phase was observed at about x≥0.05 at room temperature. Dielectric measurements revealed a gradual change from normal ferroelectric of pure BaTiO3 to highly dispersive relaxor-like characteristics in the solid solution with 30–60 mol% Bi(Mg1/2Ti1/2)O3, showing low-temperature coefficients of capacitance over a wide temperature range. The properties of Nb2O5-doped 0.85BT–0.15BMT ceramics were investigated to better understand the formation mechanism of core-shell structure, for further improving the temperature stability of the dielectric behavior.