The crystal structure of ordered perovskite BaBi0.5 3+(Bi0.25+Nb0.35+)O 3 was analyzed using electron and neutron diffraction to observe ferroelectricity with high Curie temperature. Analysis of room-temperature neutron diffraction data of BBN showed that the room-temperature structure is rhombohedral with centrosymmetric space group R3̄. Temperature dependence of powder X-ray diffraction showed that there is a structural transition between 450 and 700°C. Temperature dependent on dielectric constant and powder X-ray diffraction measurements show that ferroelectricity is consistent with a phase transition at around 420°C. Results show that room temperature rombohedral structure transforms to cubic structure at high temperature.