Density functional theory (DFT) calculations were carried out. in a study of CO and NO adsorptions on different iron site of Fe-ZSM-5. The adsorption energies and distances were similar for CO adsorption on, both small and large cluster calculations. The adsorption energies (Delta E) and enthalpies (Delta H) found for NO adsorption on [FeO](1+)-ZSM-5 and [Fe(OH)(2)](1+)-ZSM-5 clusters were in line with the previous theoretical values. Some additional energy was required for NO and CO adsorptions on [FeO](2+) -ZSM-5 (NO adsorption only), [FeOH](2+)-ZSM-5, and [Fe(OH)(2)](2+)-ZSM-5 clusters because of their positive Delta G values. The scaled vibrational frequencies for adsorbed CO and NO molecules on Fe2+,ZSM-5 cluster were computed as 1870 and 2149 cm(-1), respectively. These values are in good agreement with the experimental values for the Fe2+-CO and Fe2+-NO bands (1882 and 2140 cm(-1), respectively). Moreover, the calculated vibrational frequency (1897 cm(-1)) for NO adsorption on the [HO-FeOFe-OH](2+)-ZSM-5 cluster matches well with the experimental value (1892 cm(-1)).