(1−x)Pb(Sn 1−y Ti y )O 3 –xPb(Mg 1/3 Nb 2/3 )O 3 (x=0.1–0.4, y=0.45–0.65) ternary system was prepared using two-step columbite precursor method. Phase structure of the synthesized ceramics was studied by using X-ray powder diffraction and the morphotropic phase boundary (MPB) curve of the ternary system was confirmed. The isothermal map of Curie temperature (T C ) in the phase diagram was obtained based on the dielectric–temperature measurements. The coercive field E C and internal bias field E i were found to increase with increasing PT content, while decrease with increasing PMN content. The optimum properties were achieved in the MPB composition 0.8Pb(Sn 0.45 Ti 0.55 )O 3 –0.2Pb(Mg 1/3 Nb 2/3 )O 3 , with dielectric permittivity ɛ r , piezoelectric coefficient d 33 , planar electromechanical coupling k p , mechanical quality factor Q m and T C of being on the order of 3040, 530pC/N, 55.5%, 320 and 190°C, respectively, exhibiting potential usage for high power application.