High-resolution X-ray synchrotron powder diffraction studies under high-pressure conditions are reported for the ordered double perovskite Ba2BiSbO6. Near 4 GPa, the oxide undergoes a pressure-induced phase transition. The symmetry of the material changes during the phase transition from space group �3¯ to space group I2/m, which is consistent with a change in the octahedral tilting distortion from an a−a−a− type to a0b−b− type using the Glazer notation. A fit of the volume–pressure data using the Birch–Murnagaham equation of state yielded a bulk modulus of 144(8) GPa for the rhombohedral phase.