Using a combination of various techniques, more intermediate products could be detected during the thermal decomposition of La-2(C2O4)(3). 10H(2)O than from conventional TGA measurements. In this way a more complete and detailed decomposition mechanism is proposed. Direct identification of the intermediate phases with MT-DRIFT revealed the presence of another oxycarbonate La2O(CO3)(2). while with Hi-Res TGA a thermally unstable intermediate La-2(CO3)(3) was detected. All this information is consistent with the data obtained from TG-FTIR spectroscopic measurements.