The thermal decomposition of hafnium phosphate (both in amorphous and crystalline forms), molybdate and tungstate was investigated. Hafnium phosphate has a layered structure, that of molybdate and of tungstate are tetragonal one. On investigating these materials two main endothermic processes with mass loss were observed in the temperature range of 298–1023 K. These processes were identified as crystal and structural water loss of the materials. The total mass loss of hafnium phosphate, molybdate and tungstate was 11,35 and 6.0%, respectively. In the case of mixed hafnium-titanium salts various crystal water quantities were found, depending on the titanium content of the sample.