BaBi4Ti3MO14.5 (M = Ga, In and Sc), compounds that consist of intergrowths between the Aurivillius phase Bi4Ti3O12 and brownmillerite-like layers of BaMO2.5 were synthesized and their oxygen ion conductivities were measured using complex impedance. All three materials display a discontinuity in Arrhenius plots of their ionic conductivity. A phase transition at this discontinuity is confirmed by differential thermal analysis and is consistent with an oxygen vacancy order-disorder transition. For BaBi4Ti3ScO14.5 there is an observed hysteresis for this phase transition. At 900-degrees-C the conductivities are 2.5 x 10(2)S.cm-1 for BaBi4Ti3ScO14.5 and 4.9 X 10(-2)S.cm-1 for BaBi4Ti3InO14.5 and 4.5 X 10(-2)S.cm-1 for BaBi4Ti3GaO14.5.