The Cu-modified (Na0.5K0.5)(0.96)Li0.04Ta0.1Nb0.9O3 lead-free piezoelectric ceramics were fabricated at relatively low temperatures by ordinary sintering. The results indicate that the addition of copper oxide (CuO) does not change the crystal structure and the dielectric-temperature characteristic, but tends to slightly increase the loss tangent and significantly modify the ferroelectric and electromechanical properties. Moreover, the grains get clearly coarsened with increasing CuO content. When doped with < 0.25% CuO, the materials get softer with slightly decreased coercive fields (E-c) and increased maximum electric field-driven strains (S-m), and thus own enhanced piezoelectric properties; however, as the doping level becomes higher, the materials get harder, possessing larger E-c and reduced remanent polarization and S-m. The change in the electrical properties can be attributed to both the formation of oxygen vacancies by Cu2+ replacing Nb5+ and the modification of densification.