The thermal decomposition of freeze-dried formate precursors for copper-iron oxides was investigated by means of DTA, TG, mass spectroscopy and X-ray powder diffractometry. The freeze-dried copper formate is crystalline. Its decomposition at about 200degreesC releases formic acid (HCOOH) and carbon dioxide (CO2) as main primary gaseous decomposition products beside metallic copper as a solid product. However, the decomposition of the amorphous freeze-dried iron formate starts with a dehydration process which ends up at about 200degreesC. Further decomposition in several superimposed steps, between 220degreesC and 330degreesC, results in the delivery of: (a) HCOOH and CO2 (with reduction of Fe(III) to Fe(II)), (b) HCOOH and CO or H2CO and CO2 (without reduction). Meanwhile, several secondary decomposition products are characterized by mass spectroscopy. Regarding the complex copper-iron formate, its decomposition does not reflect only some aspects of the single formates, but also an interaction between the components which lows down the decomposition temperature. Because of the intermediate formation of metallic copper, properties of the reactive homogeneous precursor are lost and the formation of the single-phase copper iron oxides requires an annealing temperature close to that of a mixed oxide technique. (C) 2004 Elsevier B.V. All rights reserved.