A monoalkyl maleate copolymer containing pendent polyethers and carboxyls was synthesized and spread on the aqueous poly(allylamine) subphase. The polyion complexation between the spread polymer and the subphase polymer at the air-water interface and in the resulting Langmuir-Blodgett (LB) film has been studied by the surface pressure-area isotherm and Fourier transform IR (FTIR) spectroscopy. Scanning electron microscopy observation of this LB film on a porous membrane filter showed that the six-layer film was sufficiently stable to cover the filter pore (0.1 mum). An imide cross-linked LB film was achieved through heat treatment under vacuum together with concurrent removal of alkyl tails. Immersion of this film in water or in benzene did not cause any change in FTIR spectra.