Surface monolayers consisting of cationic, halogen-bridged linear platinum complex and anionic amphiphiles are formed at the air-water interface. Lipophilic polyion complex prepared from lipid and one-dimensional platinum complex is dispersed in chloroform as an indigo-colored solution, which color is ascribed to charge transfer (CT) absorption of the halogen-bridged complex (PtII→PtIV). Upon heating the solution, the indigo color disappeared due to dissociation of the linear complex into molecular unit complexes. Oriented surface monolayer is formed on water by spreading the colorless chloroform solution. Appearance of the CT band in reflectance spectra of monolayers indicates that the one-dimensional halogen-bridged complex is reformed at the air-water interface. The present technique opens an avenue to dimension-controlled organization of linear halogen-bridged complexes.