Thermal decomposition of bis(hexafluoroacetylacetonate)copper (II) hydrate in CO2/ethanol supercritical mixture is a new route to obtain homogeneous submicronic spherical copper particles without carbon contamination. A kinetic study of thermally activated decomposition reaction at 473 It of both hydrated and anhydrous complex by Visible and UV spectroscopies is reported in this paper. It was found that. at 473 K, the decomposition rate constant of the hydrated complex (1.670 min(-1)) is one order of magnitude higher than the dehydration rate constant (0.14 min(-1)). (C) 2001 Elsevier Science B.V. All rights reserved.