The topographical structures of film samples of a soluble polydiacetylenepoly[5,7-dodecadiyne-1,12-diolbis(4-butoxycarbonylmethylurethane)]solidified from its lyotropic liquid crystal phase were characterized by means of scanning electron microscopy and atomic force microscopy. The observations reveal a structural feature of extended-chain lamellae of the film samples and furthermore a three-dimensional chain segregation with respect to molecular length in a layer thinner than 5 nm on the free surface of the samples.