Structure analysis of polycrystalline BaMg1/3Ta 1/3Nb1/3O3 ceramics has been carried out using the Rietveld technique, wherein the B cations (Mg, Ta, and Nb) have the same occupancy with a size difference and charge imbalance. The compound has an ordered trigonal structure as well as a disordered cubic phase depending on the preparation temperature. The weight percentage of the ordered phase is found to increase with a rise in the calcination temperature. © Pleiades Publishing, Inc., 2006.