In a H 2 /N 2 atmosphere, the reduction processes of Mg+Fe+O and Mg+Fe+Al+O complex oxide catalysts, derived from their hydrotalcite precursors, were studied by means of temperatureprogrammed reduction (TPR). In particular, the reduction process of the Mg+Fe+O samples with a Mg/Fe ratio of 1/1 and Mg+Fe+Al+O with a Mg/Fe/Al ratio of 2/1/1 were investigated in detail in combination with in situ MoK ssbauer spectroscopy and X-ray di4raction (XRD). For the Mg+Fe+O sample, two peaks were observed in the TPR pro5le with peak temperatures at 446 and 6963C, respectively, indicating that the reduction of the oxide catalyst proceeded via two stages. MoK ssbauer spectroscopy and XRD showed that the phases in the sample were MgFe 2 O 4 and MgO before TPR. At the 5rst TPR peak (4463C), MgFe 2 O 4 was completely reduced to Mg 1؊x Fe x O. The MoK ssbauer spectrum of Mg 1؊x Fe x O exhibited a doublet with IS ؍ 0.83 mm/s and QS ؍ 0.87 mm/s. The second TPR peak (6963C) corresponded to the reduction of Mg 1؊x Fe x O to Fe 0 . For the Mg+Fe+Al+O sample, two peaks were also observed in the TPR pro5le with temperatures at 506 and 9363C, respectively. MoK ssbauer spectroscopy and XRD showed that the phases in the sample were -Fe 2 O 3 , MgFeAlO 4 , and MgO before TPR. The MoK ssbauer spectrum of MgFeAlO 4 was a doublet with IS ؍ 0.33 mm/s and QS ؍ 0.76 mm/s. At the 5rst TPR peak (5063C), -Fe 2 O 3 was reduced to Fe 2؉ and Fe 0 , while MgFeAlO 4 was transformed into Mg 1؊x Fe x O. The second TPR peak (9363C) corresponded to the reduction of Mg 1؊x Fe x O to metallic Fe 0 . E4ects of the presence of magnesium and aluminum in the solid solutions on the reduction of iron species were discussed.