The influence of pretreatments such as calcination in air, evacuation, and reduction in hydrogen at different temperatures on the stability of Fe3+ ions in the lattice of zeolite beta are reported. The concentration of Fe3+ ions in the lattice has been estimated by Mossbauer spectroscopy and ion-exchange studies. XRD and catalytic test reactions have been used to further characterize the samples. Mossbauer and ion-exchange studies indicate the formation of octahedral Fe3+ Species (defect sites) with ion-exchange capacity on calcination in air. In situ Mossbauer spectroscopy has been used to identify the various Fe species formed during the different pretreatments.