Current studies on thorium oxalate hexahydrate and its decomposition intermediates are being presented using a combination of thermal, X-ray diffraction and IR spectral methods. It has been shown here that thorium oxalate dihydrate formed by the thermal dehydration of thorium oxalate hexahydrate undergoes partial thermal decomposition to form a polynuclear complex at 165 degrees C. which further decomposes at higher temperatures to a hydroxyoxalate, a carbonate and finally to thorium oxide. Formation of thorium oxalate monohydrate and/or anhydrous thorium oxalate could not be seen here. (C) 2010 Elsevier B.V. All rights reserved.