Structural, microstructural, electrical properties and their thermal stability for (1 - x)BF-xBT system where x ranges from 0.20 to 0.35 have been investigated. Its phase diagram shows a morphortropic phase boundary (MPB) with the coexistence of rhombohedral and pseudo-cubic phases for the composition around 0.275 <= x <= 0.30. The optimized piezoelectric properties with d(33) varied from 50 to 136 pC/N and the planar electromechanical coupling factor k(p) varied from 0.165 to 0.312 over a broad high Curie temperature range from 380 to above 600 degrees C were obtained. The results indicated that samples with pseudo-cubic phase began to depole far below Curie point, while samples with rhombohedral phase showed good resistance to thermal depoling. A high thermal stability with T-d = 460 degrees C, combining a high d(33) value of 116 pC/N, was obtained in (1 - x)BF-xBT ceramics prepared by the conventional ceramic processing technique. The internal bias field in rhombohedral phase would stabilize the remnant polarization and favor the thermal stability. (C) 2012 Elsevier Ltd. All rights reserved.