Abstract Mixed nuclear μ-oxo-acetato-complexes of Mn 2+ and Fe 3+ have been synthesized by means of two different synthetic paths (precipitation or freeze drying). These complexes are interesting because after the decomposition, a manganese ferrite with spinel structure is produced. That is why the decomposition process of both substances has been investigated by means of DTA, TG and mass spectroscopy and the results compared. Water, acetic acid, carbon dioxide and acetone are identified as decomposition products and assigned to the steps of the TG graph. Quantification of the decomposition products using wet analysis methods enables a complete decomposition mechanism to be worked out.