Thallium(III) was precipitated with oxatic acid in the presence of 0.01 M In(NO3)(3) in 0.125 M HNO3. Chemical analysis of the solid obtained corresponds to the formula In[Tl(C2O4)(2)](3).12H(2)O. Thermal studies (TG, DTG and DTA) indicated the dehydration and redox decomposition of the thallic salt to the thallous salt and finally to a mixture of indium(III) and thallium(III) oxides. The latter, however, volatilised leaving indium(III) oxide as residue. Infrared absorption spectra and X-ray diffraction data were used to characterise the original salt, as well as the intermediate formed during its thermal decomposition. On the basis of these results, the compound may be represented as In3+[Tl(C2O4)(2)(H2O)(2)](3).6H(2)O.