BEA zeolite is modified by a two-steps postsynthesis method allowing incorporate iron atoms into the zeolite framework. Two series of the zeolite samples with aluminium (FexAlSiBEA) and without aluminium (FexSiBEA), containing various iron content (0.5-4.0 Fe wt.%) are obtained. For low Fe content (<2 Fe wt.%), iron is incorporated into the framework of SiBEA zeolite as a framework pseudo-tetrahedral Fe(III) as evidenced by combined used of XRD, DR UV-vis, XAS, 57Fe Mössbauer and XPS investigations. In contrast, for higher iron content, the framework pseudo-tetrahedral Fe(III) and an extra-framework octahedral Fe(III) species are identified. For FexAlSiBEA, significantly higher acidity than for FexSiBEA is evidenced by FTIR with adsorption of CO and TPD of NH3. FexAlSiBEA and FexSiBEA are found to be active and selective catalysts of N2O decomposition and selective catalytic reduction of NO with ammonia. The highest catalytic activity in both processes are obtained for the Fe4.0AlSiBEA sample containing iron mainly as the framework pseudo-tetrahedral Fe(III) and characterized by relatively high acidity.