A pyrazolonate (PMBP) of iron(III) was prepared and its metal to ligand stoichiometry was shown to be 1∶3. The decomposition of the complex was studied by thermogravimetry and differential analyses under an air atmosphere. The complex undergos two endothermic reactions without loss in mass, at 160 and 218°C, followed by an exothermic reaction at 480°C involving decomposition of the ligands. Intermediates obtained by melting of the Fe-PMBP complex were characterized by X-ray diffraction analysis. The Fe-PMBP complex was confirmed by HPLC to be a mixture of two isomers.