Piezoelectric ceramics in the ternary system (0.8-x)PbSnO 3-0.2Pb(Mg1/3Nb2/3)O3-xPbTiO 3 (PSn-PMN-PT, x = 0.42-0.47) were synthesized. Morphotropic phase boundary (MPB) compositions, located at ∼PT = 0.43-0.45 were confirmed by X-ray diffraction, dielectric, piezoelectric, and ferroelectric properties. The coercive field EC, internal bias field Ei, and mechanical quality factor Qm were found to increase with increasing PT content, indicative of piezoelectric "hardening" characteristics, while the optimum dielectric and piezoelectric properties were achieved for the MPB composition 0.36PSn-0.2PMN-0.44PT, with dielectric permittivity εr, piezoelectric coefficient d33, and planar electromechanical coupling kp being on the order of 2930, 510 pC/N and 55%, respectively. In addition, the aging behavior of the piezoelectric ceramics was studied, with aging rate of d33 ∼-6%, kp ∼-2%, εr ∼-7% per decade, respectively, similar to commercial PZT4 ceramics. © 2011 The American Ceramic Society.