The formation as well as the decomposition of magnesium chloride ammonia complexes was studied by high-pressure differential scanning calorimetry (HPDSC) and thermogravimetric analysis (TG). HPDSC runs were performed under constant ammonia pressure conditions to determine the transition temperatures and stability regions of the ammonia complexes. The TG technique has been employed to examine the stoichiometry of the complexes. The hexa-, di-and mono-ammines are proven to exist under our experimental conditions. The decomposition of the mono ammine to pure MgCl2 occurs most probably in two steps. © 2007 Springer Science+Business Media, LLC.