We have investigated the formation of as-cast thin films of a poly(styrene-block-4-hydroxystyrene) (PS-b-PHOST) copolymer spin-coated directly on topographic prepattern substrates. Either wetting or dewetting of a polymer thin film on the elevated regions occurs in the nonequilibrium state during spin-coating with solvent vapor saturated and strongly depends on the dimensions of the prepattern s. The ratio of periodic unit area to elevated one of a prepattern (3 value) is found as one of the most important factors for wettability of a thin film. The dewetting of a thin film, guided by the edges of either elevated individual periodic lines or mesas, took place with self-assembled block copolymer nanostructure when the beta value was greater than a critical value of similar to 4 in our system.