The decomposition behaviour of 0.9MgTiO(3)-0.1CaTiO(3) dielectric ceramic during a liquid phase sintering by lithium borosilicate (LBS) glass was studied. The decompositions of MgTiO3 into MgTi2O5 and Mg2TiO4 were apparent during the sintering although the reactions are thermodynamically unfavourable in glass-free compositions. The role of the LBS glass in favouring the decomposition reaction was investigated in terms of the thermodynamic activity of the reaction product in the glass. The decomposition reactions were not necessarily harmful because of the high dielectric performance of the decomposition products, MgTi2O5 (17.4 permittivity; 47,000 GHz quality factor) and Mg2TiO4 (14.4 and 55,000 GHz, respectively). (c) 2005 Elsevier Ltd. All rights reserved.