(Ba,Ca)(Ti,Sn)O₃ (BCTS) piezoelectric ceramics exhibit excellent piezoelectric properties and show great potential in the fields of piezoelectric sensors and transducers. However, their sintering temperature is very high, typically exceeding 1450 ℃, which limits their practical applications. In order to lower the sintering temperature, the oxide CuO was added into (Ba_0.95Ca_0.05)(Ti_0.90Sn_0.10)O₃ ceramics as a sintering aid in this work. Herein, BCTS-xCuO piezoelectric ceramics were prepared by the conventional solid-state sintering method, and the influence of CuO content on the sintering temperature, structure as well as dielectric and piezoelectric properties of BCTS ceramics was investigated systematically. After adding CuO, the perovskite crystal structure was mainly formed in BCTS ceramics, with a small amount of secondary phases, which may be Ba₂TiO₄ and Ba₂Cu₃O_5.9. Moreover, it was found that CuO doping can effectively reduce the sintering temperature of ceramics from 1480 ℃ to 1360 ℃ and improve the relative density of piezoelectric ceramics. The highest relative density (98.7%) and maximum average grain size (22.5 μm) were obtained at x=0.03. Hence, the optimal electrical properties were obtained at x=0.03 with piezoelectric coefficient d₃₃=573 pC/N, planar electromechanical coupling coefficient k_p=36%, relative permittivity ε_r=9467, and dielectric loss tanδ=0.021. Compared with other reported low-temperature sintered BaTiO₃-based ceramics, the x=0.03 component ceramics in this study obtained higher d₃₃ at a low sintering temperature, showing excellent comprehensive properties. In conclusion, this work demonstrates that CuO doping can successfully reduce the sintering temperature and optimize the piezoelectric properties of BCTS ceramics.