We demonstrate for the first time the complete, reversible H+/Li+ ion exchange reaction between HMO3 and LiMO3 (M = Nb, Ta) using molten LiNO3 at 320degreesC for 5 days. HMO3 were prepared from LiMO3 by ion exchange reactions using dilute HNO3. The results reveal that both LiMO3 prepared by normal solid state reaction between Li2CO3 and M2O5, and by ion exchanged from HMO3 using molten LiNO3 are isostructural. LiMO3 prepared using HMO3 yields nearly uniformly sized crystallites in contrast to those prepared by conventional solid state synthesis. The present method is simple and inexpensive compared to other methods of preparation of high purity LiMO3 powders. (C) 2002 Elsevier Science Ltd. All rights reserved.