This paper describes the phase transition behavior of a copolysiloxane (1) bearing a 4-cyanophenyl benzoate core at the terminal of the side chain. While polymer 1 exhibits only a nematic phase in bulk, it easily forms layer structures involving monolayer, trilayer, and complex multilayers at the air-water interface. In the monolayer state the cyano groups are anchored on the water surface and the aromatic moieties involving the copolysiloxane chain are directed towards the air phase. The trilayer has a partially bilayer structure on the top of the monolayer, where the layer structure was confirmed by X-ray diffraction measurement of the LB films, giving the layer spacing of 1.47 times of the calculated side chain length. Complex multilayer transitions were also observed by a further compression or changing subphase temperature.