Piezoelectric ceramics in the ternary system (0.8-x)PbSnO3-0.2Pb(Mg1/3Nb2/3)O-3-xPbTiO(3) (PSn-PMN-PT, x = 0.42-0.47) were synthesized. Morphotropic phase boundary (MPB) compositions, located at similar to PT = 0.43-0.45 were confirmed by X-ray diffraction, dielectric, piezoelectric, and ferroelectric properties. The coercive field E-C, internal bias field E-i, and mechanical quality factor Q(m) 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 epsilon(r), piezoelectric coefficient d(33), and planar electromechanical coupling k(p) 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 d(33) similar to-6%, k(p) similar to-2%, epsilon(r) similar to-7% per decade, respectively, similar to commercial PZT4 ceramics.