The thermal behaviour of alkali metal hexachlorostannates of general formula A2SnCI6 (,4 = Li, Na, K, Cs, Rb) has been studied by thermoanalytical methods (dynamic TG, DTG and DTA, and Q-TG). The compounds decompose upon heating with total (A = Li, Na) or partial (A = K, Rb, Cs) release of SnCI4 molecules to the gaseous phase. The enthalpies of the decomposition process have been evaluated on the basis of the Van't Hoff equation and using dynamic TG curves. The thermochemistry of the compounds was thoroughly examined particularly, with regard to the enthalpies of formation and crystal lattice energies, as well as enthalpy changes characterizing the dissociation process. These data revealed that stability of the compounds markedly increase with an increase in the size of alkali metal cation.