The thermal decomposition of nickel carboxylates is a feasible route to synthesize metal nanoparticles suitable for catalytic purposes. The aim of this work is the characterization of the thermal decomposition course of nickel acetate tetrahydrate, Ni(CH3COO)(2)-4H(2)O. A thermogravimetric (TGA) decomposition study carried out in three different atmospheres (air, C helium and hydrogen) showed that the dehydration of the parent salt occurs between 118 and 137 degreesC. However, irrespective of the chosen atmosphere, the sample weight loss registered in this stage remains invariable. suggesting the formation of a an intermediate basic acetate with the formula 0.86Ni(CH3COO)(2).0.14Ni(OH)(2). The dehydration step was followed at ca. 350 degreesC by the subsequent one-step major decomposition of the acetate group, producing NiO and Ni. in treatment atmospheres of air and hydrogen, respectively, but there was some indication of an additional step when the thermolysis was conducted in helium. The conclusions possible from thermal analysis were confirmed by monitoring evolved gases employing quadrupole mass spectrometry (QMS). and a set of reactions linked to the decomposition of the acetate group has been proposed to account for most of the gas products detected. X-ray photoelectron spectroscopy (XPS) was used to investigate the solid phases obtained during the thermal decomposition of the salt in He atmosphere. (C) 2004 Elsevier B.V. All rights reserved.