Barium titanate (BaTiO 3 ) powders were synthesized from commercially available raw materials (BaCO 3 and rutile) without particular mechanochemical processing by solid-state reactions in water vapour atmosphere. The formation rate of BaTiO 3 was accelerated by water vapour and single phase of BaTiO 3 was obtained by calcination at 700 โข C for 4 h in water vapour atmosphere, though high temperature (850 โข C for 2.5 h) was required by calcinations in air to complete the reaction. The formation kinetics followed the Valensi-Carter equation, which suggested that the reaction proceeded by a diffusion controlled process. The apparent activation energy for the formation of BaTiO 3 in air and water vapour atmosphere was estimated to be 361 ยฑ 20 kJ/mol and 142 ยฑ 17 kJ/mol, respectively. Water vapour is considered to enhance thermal decomposition of BaCO 3 and formation of BaTiO 3 by attacking surface Ti-O-Ti bonds in TiO 2 , increasing partial pressure of Ba(OH) 2 , and producing vacancies in the BaTiO 3 structure.