Thermal transformations of Co(H2PO4)(2).2H2O in air, vacuum, water-vapor atmosphere were studied by the methods of DTA, XRD, paper chromatographic analyses and gravimetry. It was established that the removal of the water of crystallization is accompanied by the processes of anionic condensation and disproportionation when dihydrate is heated in air. It was also shown that X-ray-amorphous anhydrous cobalt dihydrogenphosphate is forced only in vacuum under isothermal conditions. The kinetic characteristics of this reaction were obtained and the possibility of proceeding of dehydration-rehydration processes in cyclic regime was studied.