Thermal analysis of zinc hexa(formato)ferrate(III) decahydrate, Zn₃ [Fe(HCOO)₆]₂ 10H₂O has been investigated up to 800°C in static air atmosphere employing TG, DSC, XRD, IR, ESR and Mössbauer spectroscopic techniques. After dehydration at 160°C, the anhydrous complex decomposes into α-Fe₂ O₃ and zinc carbonate in successive stages. Subsequently the cations remix to yield fine particles of zinc ferrite, ZnFe₂ O₄ , as a result of solid state reaction between α-Fe₂ O₃ and zinc carbonate at a temperature (600°C) much lower than for ceramic method.