Dehydration of inorganic crystallohydrates (Fe2F x 7.1H2O, FeF3 x 3.82O, CoF2 x 4H2O, and NiF2 x 4.4H2O) in the conditions of microwave treatment (MWT) is studied. It is shown that in all cases the MWT changes the defectness of crystals, as well as their thermal stability. The dehydration schemes for the compounds above are presented.