This study is the first approach to analyze hydrazine (N2H4) in aqueous solution as well as adsorbed on catalyst surfaces by NIR (near-infrared) spectroscopy. N2H4 molecule was observed at 4961 cm(-1) in basic solution and hydrazinium ion (N2H5+) was observed at 4767 cm(-1) in acidic solution. N2H5+ formed on the Bronsted acid sites of H+/ZSM-5 and N2H5 delta+ species were observed on SiO2. In contrast, bidentate N2H4 species were proposed on the basic MgO and LDH surfaces.