Trinuclear μ3-oxo clusters have been widely studied in the last decades due to their structural particularities and their large spectrum of properties [1]. An important role in the application of this class of compounds plays the possibility of synthesis of iron oxide and mixed iron oxides nanoparticles [2-3]. In this study we report the study of two trinuclear iron based clusters with the composition [Fe3O(C4H3OCOO)6(CH3OH)3]·NO3·2CH3OH (1) [4] and [Fe2CrO(C4H3OCOO)6(CH3OH)3]·NO3·H2O (2) by the thermogravimetric method. The thermal analysis study (Figure 1) shows that the decomposition of complexes occurs in several steps with the formation of corresponding iron oxides Fe3O4.5 and Fe2CrO4.5. Figure 1: Thermoanalytic curves for [Fe3O(C4H3OCOO)6(CH3OH)3]·NO3 (left) and [Fe2CrO(C4H3OCOO)6(CH3OH)3]·NO3·H2O (right) measured at air in the 20 – 1000 °C temperature range at a 10 °C/min speed. Both compounds are stable only up to 50 °C after what begins the decomposition process through the elimination of solvent molecules (water and methanol) in the temperature range 50 – 160 °C. At higher temperatures occurs the furoate ligand decomposition up to 400 °C. The final products are obtained at 400 °C as iron oxide Fe3O4.5 for 1 and mixed iron chromium oxide Fe2CrO4.5 in the case of 2.