(Na(0.5)K(0.5))NbO(3)-based materials are promising lead-free piezoelectrics because of their relatively high Curie temperatures and piezoelectric coefficients. Using precursor powders made by a coating method, (Na(0.5)K(0.5))(0.945)Li(0.055)Nb(0.96)Sb(0.04)O(3) thick films were successfully fabricated by pressureless sintering. Large high-field -d(31) value of 1700 pm/V, > 20 times larger than that of the bulk counterpart, was observed at an applied dc electric field of 6-8 kV/cm. In situ X-ray diffraction study showed that the large piezoelectric response was partially due to non-180 degrees domain switching under the electric field. Further investigation is needed to elucidate this enhancement effect. The enhanced high-field piezoelectric property observed should encourage the use of lead-free piezoelectrics.