Fe-substituted mordenites were synthesized hydrothermally, partially substituting iron atoms for the framework aluminum of mordenite. XRD, SEM, IR, UV-VIS DRS, ESR, XAS, and catalytic activity studies provided the evidence of Fe^(3+) present in the zeolite framework. The framework IR bands were shifted to lower frequencies as Fe^(3+) ions incorporated into the lattice, and a new Si-O-Fe bond vibration was located near 668 cm.1. The presence of a signal at g=4.3 in the ESR spectra was assigned to Fe^(3+) isomorphously substituted in the tetrahedral position. EXAFS at the Fe K-edge revealed that the Fe^(3+) ions were present in the zeolite framework in a four-fold coordination with an average Fe-O distance of 1.86 A. In the UV-vis spectra, an absorption was observed at 375.7 nm which was assigned to the presence of Fe^(3+) in the zeolite framework. A toluene alkylation study reflected that the acidity strength of mordenite is weakened due to the presence of lattice iron species.