The thermal decomposition of iron(II) oxalate–magnesium oxalate mixture (2:1 mole ratio) was investigated using DTA-TG, XRD and Mössbauer effect measurements. The decomposition of the anhydrous oxalate mixture proceeds in two steps and kinetic analysis of the two steps were performed under non-isothermal conditions using different integral methods of analysis. Integral composite analysis of data showed that the decomposition reactions are best described by the three-phase boundary, R3 model. Kinetic analysis of data were also carried out in accordance with the methods of Ozawa and Coats-Redfern and the results are discussed in comparison with the composite analysis of data. Mössbauer spectra of samples calcined at different temperatures are discussed and show that in the early stages of the decomposition at about 300 °C, part of the Fe(III) oxide is formed in superamagnetic doublet state. As the temperature is increased, supermagnetism disappears. The results of XRD analyses are in accordance with the results of the Mössbauer effect and show that magnesium ferrite forms in samples heated at higher temperatures.