The adhesion of UV-cured coatings to ceramics, metals or plastics is very poor compared with heat-cured coatings, especially after exposure to high humidity and immersion in water. The effects of base resins, reactive diluents, photosensitisers and coupling agents on adhesive strength of UV-curable resins were examined. Adhesion, especially after absorbing water, depends mainly on the concentration of photoreactive functional group, (the methacryloyloxy group) of the base resin molecules and the nature of the functional group of reactive diluents. For example, the addition of monofunctional diluents containing hydroxyl groups improves the adhesive strength of the resins, whereas multifunctional diluents do not. Coupling agents with amino groups are also effective. The mechanisms of improved adhesive properties are discussed. -- AATA