Lead magnesium niobate-lead titanate (referred to PMN-PT or PMNT) is a very attractive material for the applications in multi-layer capacitors and electro-mechanical transducers. This material has unusually high dielectric permittivity, low dielectric loss and high strain around Curie temperatures. Niobium oxide, one of the components for fabricating PMNT, always contains tantalum impurity. It was originally thought that to make high quality PMNT, it was necessary to use high purity niobium oxide. High purity niobium oxide is very costly. Therefore, it limits massive application of this material. If Ta-doping in PMN-PT does not significantly degrade the properties, it will lower the cost for large-scale industrial production and make the materials more applicable. Our previous work shows that an appropriate amount of tantalum doping in 0.9PMN-0.1PT significantly increases the dielectric constant and refine the grain size. In this work we extend the investigation to 0.65PMN-0.35PT and 0.70PMN-0.30PT that are more close to the morphotropic phase boundary (MPB). (C) 2002 Elsevier Science B.V All rights reserved.