BiFeO3-BaTiO3 (BF-BT) solid solutions are lead-free candidates for high-temperature piezoelectric applications. BF-BT ceramics with compositions near the morphotropic phase boundary (MPB) separating rhombohedral (R) and pseudo-cubic (PC) phases were fabricated by the conventional high temperature sintering method, and their thermal stability and aging properties were studied in detail. BF-BT ceramics with rhombohedral (R) phase show much better thermal stability and aging properties than those with pseudo-cubic (PC) or coexistence of PC and R phases. The thermal degradation and aging rates of BF-BT ceramics with R phase are on the order of 1% and 1.2% per decade, respectively. X-ray diffraction results reveal that the domain state of poled rhombohedral BF-BT ceramics is stable up to its Curie temperature, which is responsible for the high thermal stability. The Rayleigh analysis shows that the low aging rate is attributed to the low domain wall contribution to the overall piezoelectric response. The high thermal stability and low aging rates indicate that the lead-free BF-BT ceramics with R phase are potential candidates for sensor and transducer applications over a broad temperature range.