Selected composition ceramics in the Pb(Mg1/3Ta2/3)O-3-PbTiO3 system were prepared and characterized. Phases developed in the B-site precursor and perovskite systems were examined by X-ray diffraction. Dependencies of the lattice constants and dielectric properties upon composition were investigated. Dielectric relaxation modes in the paraelectric temperature range were quantitatively analyzed in terms of diffuseness parameters. Ferroelectric hysteresis responses with changes in temperature were monitored. Dielectric maximum temperatures in the system increased steadily with increasing PbTiO3 concentration, whereas maximum dielectric constants were higher at intermediate compositions.