The kinetics of isothermal-isobaric dehydration of Li5P3O10·5H2O in vacuum (p=10−1 hPa) and in water vapour atmosphere (
=23·hPa) was investigated by TG in the temperature range 40–140°. It was shown that the initial non-degradation removal of 1/10 of the crystal water, the rate of which is sensitive to
, proceeds according to the laws of reversible topochemical reactions. In the next, irreversible degradation stage, where the bulk of the crystal water is removed, the kinetic characteristics of the process and the DSC effects exhibit a low sensitivity to the water vapour pressure. The peculiarities of Li5P3O10·5H2O dehydration were considered in comparison with the thermal behaviour of Na5P3O10·6H2O and K5P3O10·4H2O.