A complex precursor has been synthesized by dissolving copper oxalate in liquor ammonia followed by drying. The thermal decomposition of the precursor has been studied in different atmospheres, air/nitrogen. The mechanism of decomposition of the precursor in air is not as simple one as in nitrogen. In nitrogen, it involves endothermic deammoniation followed by decomposition to finely divided elemental particles of copper. Whereas in air, decomposition and simultaneous oxidation of the residual products (oxidative decomposition), make the process complex and relatively bigger particle of cupric oxide are obtained as final product. The products of decomposition in different atmospheres have been characterized by X-ray diffraction and particle size analysis. The stoichiometric formula, Cu(NH3)(2)C2O4 of the precursor is established from elemental analysis and TG measurements, and it is designated as copper amino oxalate (CAO).In nitrogen atmosphere, the deammoniation and decomposition have been found to be zero and first order, respectively. The values of activation energy have been found to be 102.52 and 95.38kJ/mol for deammoniation and decomposition, respectively. (C) 2003 Elsevier B.V All rights reserved.