Ceramic samples with compositions along the (1 – 2x)BiScO3·(2 – y)xPbTiO3∙yxPbMg1/3Nb2/3O3 (y = 1.2, 1.0, 0.9, 0.5) sections in the BiScO3–PbTiO3–PbMg1/3Nb2/3O3 (BS–PT–PMN) system have been characterized by X-ray diffraction and dielectric, piezoelectric, and thermally stimulated depolarization current measurements. The materials with 1 – x ≲ 0.5 have been shown to consist of perovskite solid solutions. With increasing BS content, the symmetry of the solid solutions rises from tetragonal to cubic. In the intermediate composition region (morphotropic region (MR)), the samples consist of a mixture of solid solutions differing in symmetry. We have located the MR boundaries and examined the effect of composition on the dielectric and piezoelectric properties of the solid solutions. [ABSTRACT FROM AUTHOR]