The PbSnO3-PbTiO3-Pb(Mg1/3Nb 2/3)O3 (PST-PMN) ternary system with morphotropic phase-boundary (MPB) compositions were fabricated using a two-step columbite precursor method. The effects of Al2O3 and MnO2 addition on the dielectric, piezoelectric, and ferroelectric properties of PST-PMN were investigated. MnO2 acted as an acceptor dopant and induced a "hardening" effect in PST-PMN, with decreased piezoelectric coefficients d33 and increased mechanical quality factors Q m, while the addition of Al2O3 led to the significant decrease of piezoelectric properties, attributed to the second phase. Of particular interest is the fact that the Mn-doped PST-PMN exhibited excellent properties when the doping level was in the range of 0.2-0.5 wt%, with piezoelectric d33, planar electromechanical coupling kp, dielectric permittivity Ïμr, Qm, remnant polarization Pr and coercive field EC being on the order of ∼510 pC N-1, ∼57%, 3120-3500, 530-600, 27-30 μC cm -2, and ∼8 kV cm-1, respectively, showing advantages over commercial PZT4-type ceramics, which are promising for high-power electromechanical applications. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.