The photo-induced grafting copolymerization of N-vinyl-2-pyrrolidone (NVP) to segmented polyetherurethane (SPEU) was studied. The experiments in this work were performed at nitrogen atmosphere and room temperature by using UV light.The effects of concentration of N-VP and light sensitive agent DMT in the grafting solutions and irradiation time on the grafting yield in acid and basic mediums were investigated. The swelling behavior of modified films in water was followed and the surface structure of the films was observed by scanning electron microscope. All the results showed that this kind of photo-induced grafting occured successfully in al-kaline medium. The reason of the alkaline effect was discussed briefly.