Amidoxime resins were derived from poly(acrylonitrile-co-vinylidene chloride-co-divinyl-benzene) beads, which were prepared by suspension polymerization of the ternary monomeric mixtures in the presence of 4-methyl-2-pentanone (MIBK) or 1,2-dichloroethane (DCE) as the diluent (porogen), in order to clarify the effect of copolymerized vinylidene chloride on properties of the resulting amidoxime resins. Pore structure analyses of the copolymers as well as of their amidoximated derivatives clarified that MIBK yields larger pores than does DCE and then the latter gives large specific surface areas than does the former. On the other hand, chemical properties of the amidoximated resins, such as anion-exchange capacities and uranyl ion uptake, were not essentially affected by the diluent species, indicating that both MIBK and DCE as the porogen lead to the amidoxime resins with almost the same ability in recovery of uranium from sea water. The uranium recovery decreased with increase in the vinylidene chloride content, but the decrease in the recovery was minor up to the 10 mol % of vinylidene chloride. It was also clarified that the uranium recovery by the amidoxime resins containing vinylidene chloride is greatly enhanced by the alkali treatment.