In order to characterize the interface in polymer blends, a new method is suggested, in which the interface is exposed by selectively dissolving in solvent. By means of X-ray photoelectron spectrometry, we studied the molecular state in the interfacial area of graft copolymers of polyolefin and polar polymer. When the graft copolymers were used as compatibilizers, the backbone polymer and branch polymer diffused into the corresponding miscible polymer bulks. The specific interactions between some macromolecules were very strong; the small solvent molecule could not separate these macromolecules.