The structures and the photoisomerization of polyion complex Langmuir-Blodgett (LB) films of an amphiphile bearing two azobenzene units were studied, The anionic amphiphile was spread on the aqueous subphases with and without polycations. The area per molecule depended on the polycation species and was larger than that of pure amphiphile for three polycations out of four, It was suggested that the area per molecule is determined by the compromise between the various intermolecular interactions involved in the formation of the monolayer, The LB transfer was possible for all the polyion complex systems and reversible photoisomerization was observed for all the LB films by alternate UV and visible light irradiation, As the area per molecule where the LB transfer was conducted increased, the fraction of the cis isomer at the photostationary state with UV light irradiation increased, suggesting the role of free volume in the trans-to-cis photoisomerization.