The adsorption of NO and NO2 and their subsequent reduction by hydrazine monohydrate (HDM) over Fe-BEA zeolite were investigated using an FT-IR spectrophotometer equipped with an in-situ cell. Although NO and NO2 molecules were adsorbed on Fe species in an unaltered state, some of them reacted with oxygen atoms, resulting in the adsorption of NO2 and NO3-, respectively. The reducing species that had originated from HDM on Fe-BEA selectively reduced these molecules to N2, while a small amount of N2O was formed in the reduction of NO by HDM. NO and NO2 were rapidly reduced by HDM through their adsorbed state even at 150 ℃, and Fe species were required for their adsorption and for the formation of reducing species from HDM.