Environmental responses of a polystyrene, PS, surface layer formed on a poly(vinyl alcohol), PVA, sublayer were studied. The thin organic surface was prepared by casting the solution of a copolymer consisting of covalently-connected PVA and PS segments, PVA-PS graft copolymer. X-ray photoelectron spectroscopic inspection of the graft copolymer sample films confirmed the formation of a surface layer of the PS component of a thickness of a few tens of angstroms. By changing the surface contacting medium from air to water at 25-degrees-C, which is significantly below the T(g) of the PS segment, an unexpected dynamic surface rearrangement was observed by means of a contact angle measurement with an air-in-water technique, where the contact angle changed from one similar to the PS homopolymer to one close to the PVA homopolymer within a 1-3-h period. At 10-degrees-C, in contrast, the environmental response was strongly suppressed. The graft copolymer film was immersed into water to effect surface rearrangement, recovered, dried at 120-degrees-C, i.e., above the T(g) of the PS segment, and found to restructure itself reversely to the original surface state, while at 60-degrees-C the reverse process was found to be incomplete.