Ferroelectrics 0.67Pb (Mg1/3Nb2/3)O-3-0.33PbTiO(3) (PMN-PT) + x mol% WO3 (x=0.1, 0.5, 1, 2) were prepared by columbite precursor method. Electrical properties Of WO3-modified ferroelectrics were investigated. X-ray diffraction (XRD) was used to identify crystal structure, and pyrochlore phase were observed in 0.67Pb (Mg1/3Nb2/3)O-3-0.33PbTiO(3)+ 2 mol% WO3. Dielectric peak temperature decreased with WO3 doping, indicating that W6+ incorporated into PMN-PT lattice. Lattice constant, pyrochlore phase and grain size contribute to the variation of K-max. Both piezoelectric constant (d(33)) and electromechanical coupling factors (k(P)) were enhanced by doping 0-1 mol% WO3, which results from the introduction of "soft" characteristics into PMN-PT, while further WO3 addition was detrimental. We consider that the two factors, introduction of "soft" characteristics and the formation of pyrochlore phase, appear to act together to cause the variation of piezoelectric properties of 0.67PMN-0.33PT ceramics doping with WO3 (C) 2003 Elsevier Ltd. All rights reserved.