Phase transitions, melting processes and thermal decompositions of [Ba(H2O)(3)](ClO4)(2) and [Ba(NH3)(4)](ClO4)(2) were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis connected With quadruple mass spectrometer (TGA/QMS). The phase transition at T-c(h) = 304.0 K (on hearing) and at T-C(c) = 286.8 K (on cooling) was detected for [Ba(NH3)(4)](ClO4)(2) by means of DSC, but none phase transition at that temperature range has been registered for [Ba(H2O)(3)](ClO4)(2). The decomposition process of the [Ba(H2O)(3)](ClO4)(2) supervene in the three main stages. In stage 1 (305-520 K) dehydration of [Ba(H2O)(3)](ClO4)(2) to anhydrous Ba(ClO4)(2) undergoes ill two steps, in which consecutively 1/3 (at 305-360 K) and 2/3 (at 361-520 K) of all H2O molecules are liberated. In stage II (521-740 K) anhydrous Ba(ClO4)(2) has two solid-solid phase transitions: at T-C1 = 566.6 K and at T-C2 = 641.7 K. Next it melts at T-m = 760 K. Stage III (above 761 K) is connected with decomposition and explosion of melted Ba(ClO4)(2). The decomposition process of the [Ba(NH3)(4)](ClO4)(2) supervene in the three main stages, too. Stage I (310-520 K) is connected with deammination of [Ba(NH3)(4)](ClO4)(2) to Ba(ClO4)(2) and all NH3 molecules are liberated. Stages II and III (521-850 K) are exactly the same as they were observed for [Ba(H2O)(3)](ClO4)(2). (C) 2009 Elsevier B.V. All rights reserved.