The kinetics of the thermal dehydration of crushed crystals of CaCu(CH3CO2)(4) . 6H(2)O in a flowing nitrogen atmosphere have been studied by means of isothermal gravimetry. At higher temperatures than 85 degrees C the dehydration seemed to be described by three-dimensional phase boundary reactions, R(3)(alpha). At temperatures lower than 80 degrees C, the initial part of the dehydration could be described by phase boundary reactions, R(3)(alpha), that of the middle part follows the Avrami-Erofeev type reaction, A(2.5)(alpha), and then the kinetics of the final part followed diffusion-controlled models. These transitions of the dehydration mechanisms have been discussed on the basis of the diffusion process of dissociated water molecules.