Polycrystalline samples of Bi(Mg0.5Ti0.5)O3-PbTiO3 (BMT-PT) solid solutions exhibit high ferroelectric Curie temperatures and are promising materials for high temperature piezoelectric devices. A morphotropic phase boundary (MPB) between ferroelectric rhombohedral and tetragonal phases occurs between BMT-PT ratio of 70-30 and 65-35 compositions. In the present investigation, ceramics having BMT-PT ratios in the range from 70-30 to 50-50 were prepared by a conventional solid state reaction method. The change of crystal structure as a function of composition and temperature has been studied using high temperature X-ray diffraction. Polarisation-Electric field hysteresis curves at different temperatures show antiferroelectric behaviour for x = 0.30, 0.35 and 0.40 compositions while 0.45 and 0.50 show a ferroelectric behavior.