We have characterized, with emphasis on XAFS spectroscopy, one of the most promising DeNOx catalysts, i.e., Fe/ZSM5 prepared through the FeCl3 sublimation technique. XAFS is a very useful tool for this purpose since it is element specific and can be used in situ, namely, in the presence of the reactants and at reaction temperature. In this communication it will be pointed out that the as-synthesized Fe/ZSM5 catalyst contains stable binuclear iron oxo/hydroxo-complexes. The reaction of these complexes with the probe molecule CO clearly shows that only one of the oxygen shells around iron changes while the iron contribution is not affected, the iron complex remaining binuclear.