X-ray structure analysis of BaMg1/3(Ta,Nbx)2/3O3 ceramics revealed that BaMg1/3Ta2/3O3 (BMT) has an ordered trigonal phase as well as a disordered cubic phase depending on the preparation temperature. Complete ordered phase for BaMg1/3Nb2/3O3 (BMN) has not been observed. The ordering of Mg, Ta and Nb cations has dependence on the size, charge difference and calcination temperature. © 2002 Elsevier Science B.V. All rights reserved.