Pb(Zr 0.52 Ti 0.48 )O 3 –Pb(Mg 1/3 Nb 2/3 )O 3 –Pb(Zn 1/3 Nb 2/3 )O 3 ceramics were prepared using the conventional mixed-oxide route. The effects of CuO addition on the phase transition and electrical responses were investigated. X-ray diffraction analysis indicated that the phase of the material changed from an rhombohedral structure to a MPB structure and then a tetragonal structure when the CuO content was increased from 0.00 to 0.30wt.%. The P–E hysteresis loops of CuO-doped PZT–PMN–PZN ceramics showed pinched shapes instead of the normal square-like P–E loops. The pinched loops were assumed to be the result of the pinning effect of the defect dipoles. Optimized electrical properties, such as d 33 =280pC/N, k p =0.53, tanδ=0.0090, Q m =1645 and ɛ r =982, were achieved by doping 0.20wt.% CuO in PZT–PMN–PZN ceramics sintered at 920°C.