Low-temperature sintering of 0.25PMN–0.40PT–0.35PZ ceramics was investigated using CuO as a sintering aid. Effect of CuO on the sinterability, microstructure, and electric properties of 0.25PMN–0.40PT–0.35PZ system was systematically studied. The CuO addition significantly reduced the sintering temperature of 0.25PMN–0.40PT–0.35PZ from 1260°C to 950°C. SEM results indicated that a dense microstructure without any second phase was obtained when the amount of CuO was 0.25 wt%, which gave rise to high values of d33 = 532 pC/N and kp = 58.4%. A large field-induced longitudinal strain ~2.28% (at 30 kV/cm) can also be obtained for 0.25 wt% CuO-added specimens, which shows a great promise for multilayer actuator applications.