The behavior of monolayers of poly(amic acid) alkylamine salts containing different dimethylsiloxane chain lengths at the air-water interface was investigated. The limiting areas estimated from surface pressure-area isotherms were much larger than those calculated from both the alkyl chain number per repeating unit and the cross-sectional area of the alkyl chain. The direct observation of monolayers was carried out by Brewster angle microscopy (BAM). The BAM observation was affected by the length of the dimethylsiloxane chain in the poly(amic acid)s. The layered structure of the LB films of poly(amic acid) alkylamine salts with multichains was investigated by X-ray diffraction, Fourier transform infrared-reflection absorption spectroscopy, and X-ray photoelectron spectroscopy. Consequently, it was found that the LB films consist of bilayer (Y-type) structures in which the alkyl chains are appreciably tilted from the normal direction and that the long dimethylsiloxane chain is concentrated in the outer surface of the LB films.