(1 − x)(0.85Bi0.5Na0.5TiO3–0.11Ba0.5K0.5TiO3–0.04BaTiO3)- xK0.5Na0.5NbO3 lead-free piezoelectric ceramics with x = 0.00, 0.02, 0.03, 0.04, 0.05, and 0.10 were prepared by a conventional solid state method. A coexistence of rhombohedral (R) and tetragonal (T) phases was found in the system, which tended to evolve into pseudocubic symmetry when x increases. The x = 0.04 sample exhibited improved electrical properties: the dielectric constant εr = 1900 with the low loss tangents 0.06, the Smax/Emax of ~400 and ~460 pm/V under unipolar and bipolar electric field, respectively. Meanwhile, piezoelectric constant d33 still maintained ~160 pC/N. These could be owed to the formation of polar nanoregions for relaxor phase.