Indium(III) was precipitated with oxalic acid in the presence of ammonium nitrate maintaining an over all concentration of 0.125 M in HNO3. The chemical analysis of the complex salt obtained corresponded with the formula, NH4[In(C2O4)(2)]. 2H(2)O. Thermal decomposition studies of the complex indicated the formation of intermediates: ammonium indium oxalate and indium(III) oxalate and the final product to be indium(III) oxide. The isothermal decomposition, infrared absorption spectra, and X-ray diffraction patterns have been used to characterise the complex and the intermediate product of thermal decomposition.