Er 2 O 3 (0–0.8wt.%)-doped 0.82Bi 0.5 Na 0.5 TiO 3 –0.18Bi 0.5 K 0.5 TiO 3 (BNKT18) lead-free piezoelectric ceramics were synthesized by a conventional solid-state reaction method. The effects of Er 2 O 3 on the microstructure and electrical properties were investigated. X-ray diffraction (XRD) data shows that Er 2 O 3 in an amount of 0.2–0.8wt.% can diffuse into the lattice of the BNKT18 ceramics and form the pure perovskite phase. Scanning electron microscope (SEM) images indicate that the grain sizes of BNKT18 ceramics decrease with the increase of Er 2 O 3 content; in addition, the modified ceramics have the clear grain boundary and a uniformly distributed grain size. At room temperature, the electrical properties of the BNKT18 ceramics have been improved with the addition of Er 2 O 3 , and the BNKT18 ceramics doped with 0.6wt.% Er 2 O 3 have the highest piezoelectric constant (d 33 =138pC/N), the highest planar coupling factor (k p =0.2382), the highest remnant polarization (P r =25.2μC/cm 2 ), the higher relative dielectric constant (ε r =936) and lower dissipation factor (tanδ=0.047) at a frequency of 10kHz. Moreover, the T m and T d of the samples increase with the addition of Er 2 O 3 .