Urethane acrylate anionomers(UAA) were prepared in various compositions by three steps. Under UV radiation, UAA formed pH-sensitive films with drying film thicknesses of 60, 200 and 330μm. The equilibrium swelling ratios(SR) of the films in various pH buffer solutions increased with the increase of the molecule weight of UAA. The influence of the film thicknesses on the swelling performances of the films was investigated. The film with a thickness of 60 μm could reach the equilibrium state in 2.5-3.5 min. A high SR was obtained for a thick film due to its low average network density. The cured film could swell reversibly and rapidly with the change of pH, which is important for a controlled release system.