Abstract: This invention discloses a composite resin prepared by reacting a monool (a) containing a C25-200 hydrocarbon group; a multifunctional compound (G) containing a functional group capable of reacting with a hydroxyl group of the monool (a) and a compound (H) having a functional group capable of reacting with the functional group in the multifunctional compound (G) as well as uses thereof. The composite resin of the invention serves as an excellent interface modifier upon incorporation into a film-coating material such as ink or paint or into a molding material. The modifier can modify not only the interface between the film-forming material or the like and a base material but also the surface of the film-forming material, that is, the interface between the film-forming material and the air.