The monolayers of amino acid amphiphiles at the air-water interface on pure water and ion-containing subphases have been studied using infrared reflection-absorption spectroscopy. It is the first time that the NH stretching signals are detected from the monolayers at the air-water interface with this technique. In the presence of Ag+ and Pb2+ in the subphases, the covalent interaction between metals and carboxylate groups is predominant in the form of chelating and/or bridging bidentate coordination, and the intermolecular hydrogen-bonding interaction between the adjacent molecules through amide groups is increased in comparison with that in the case of pure water. In the presence of Ca2+ and Cu2+, the ionic interaction between metal ions and carboxylate groups is preferred, and the intramolecular hydrogen bond is developed. The hydrogen bond in the monolayers at the air-water interface undergoes an obvious change in type and strength depending on metal ion in the subphase.