Porous amidoxime hollow fibers, which were prepared by radiation-induced graft polymerization of acrylonitrile onto porous polyethylene hollow fibers and subsequent amidoximation, were used as packing materials of the adsorption bed for uranium recovery from seawater. Seawater was forced to flow through the bed charged with the amidoxime hollow fibers either by pumping or by ocean current. Uranium concentration decay through the bed could be well correlated with residence time based on the adsorption rate expressed in terms of the overall mass-transfer coefficient. The resultant activation energy of 20 kcal/mol for uranium adsorption was indicative of the chelate formation of the amidoxime group with uranyl species as a rate-determining step.