Monooctadecyl maleate and monooctadecyl itaconate copolymers containing pendent oligoethers and carboxyls were synthesized and spread on pure water, on the aqueous poly(allylamine), and on saturated aqueous NaCl. Examination of the monolayer properties of the polymers by surface pressure-area isotherms reveals that their pendent oligoethers lie at the air-water interface at low surface pressures and are forced down into the subphase when the film is compressed. This orientation switching by compression-expansion cycle of monolayers is reproducible. Another pendant of carboxyls makes these polymers possible to form the polyion-complexed monolayers with the subphase polymer poly(allylamine) at the air-water interface. The polyion-complexation at the air-water interface and in resulting Langmuir-Blodgett film was confirmed by the surface pressure-area isotherm and FT-IR spectroscopy, respectively. SEM observation of these films on a porous membrane filter showed that the six-layer film was sufficiently stable to cover the filter pore(0.1 mu m).