Samples of piezoelectric PT-1 ceramics based on PbTiO3 modified by Ca, Nd, Bi and Mn have been studied. The poling d.c. and strong a.c. field effect on the domain structure and electrical and physical properties (eT33/e0, sE11, d33, d31, anisotropy d33/d31) has been determined. The formation of closed domain structures with laminar series of 90° domains was established for “virgin” ceramics. The orientation of 90° domain boundaries normal to the electric field direction was found to take place under the strong a.c. field. The further application of the d.c. poling field leads, mainly, to 180° domain reorientations that manifests itself in the rapid increase of piezoelectric coefficients and anisotropy under the relatively weak poling fields. It was established that the increased piezoelectric anisotropy is due to 180° and 90° domain reorientations.