Powders of a Pb[(Zn1/3Ta2/3)(0.2)(Zn1/3Nb2/3)(0.6)Ti-0.2]O-3 system with gradual replacement of Zn by Mg were prepared by employing a B-site precursor method and developed structures were studied by X-ray diffractometry. Dielectric properties of the sintered ceramics were characterized under weak-field low-frequency conditions. A high maximum dielectric constant value of 38,000 (@ 1 kHz) was realized when 3/4 of octahedral Zn was replaced by Mg. Field-dependent polarization responses were also monitored at various temperatures to investigate ferroelectricity. Microstructures of the fractured ceramics were examined using a scanning electron microscope. (C) 2003 Elsevier Ltd. All rights reserved.