In this study, 0.96(K 0 .5 Na 0.5 )NbO 3 -0.04LiNbO 3 (KNLN) + x wt.%CuO piezoelectric ceramics, where x = 0.0, 0.1, 0.2, 0.25, and 0.30, have been successfully fabricated using the conventional solid-state reaction method. The effect of CuO on the sintering behavior, structure, microstructure, and electrical properties of KNLN ceramics was studied. The addition of CuO reduced the sintering temperature of the ceramics from 1 050 °C to 950 °C. The experimental results showed that with CuO doping, the KNLN ceramics can be well sintered at a low temperature and show a dense, pure perovskite structure. At a sintering temperature of 950 °C and CuO content of 0.25 wt.%, the best physical properties of the ceramics, such as density ( ρ ), 4.14 g cm −3 ; electromechanical coupling factors ( k p ), 0.33 and ( k t ), 0.43; dielectric constant ( ∊ ), 349; dielectric loss (tan δ ), 0.008; mechanical quality factor ( Q m ), 133; and piezoelectric constant ( d 33 ), 130 pC N −1 , were obtained.