The mixture of BaCO3 and rutile-type TiO2 powders mixed with wet ball-milling was calcined in air and the phase change in calcination process was investigated in detail. The slow heating in the temperature range from 800 to 850 degrees C was effective to change BaTiO3 to BaTi2O5 in the following heating process. The influence of two factors in calcination for the synthesis of BaTi2O5, which are temperature profile with slow heating and packing state of the mixture, was investigated. The slow heating in two temperature ranges, 800-850 degrees C and 1100-1160 degrees C, was effective for the synthesis of BaTi2O5. The production amount of BaTi2O5 was increased by using powder compacts rather than powder form. By calcining powder compacts at 1160 degrees C for 2 h, the powder of BaTi2O5 having an alpha(s) value of 0.93, which is semi-quantitatively corresponding to BaTi2O5 production ratio, was obtained. (C) 2013 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.