At Tokyo Electric Power Company (TEPCO) Fukushima Daiichi nuclear power plant (NPP), water contaminated with radionuclides such as Cs-137 and Sr-90 has been stored in tanks and seawater-intake area. We have prepared cobalt-ferrocyanide-impregnated fibers via four steps: the grafting of an epoxy-group-containing monomer, the conversion of the epoxy group into positively charged groups, the binding of ferrocyanide ions ([Fe(CN)(6)](4-)), and the precipitation of cobalt ferrocyanide (Co-2[Fe(CN)(6)]) by contact with cobalt ions. However, the impregnation structure of cobalt ferrocyanide microparticles onto the fiber remains unclear. Here, we describe the impregnation structure from the results of rebinding [Fe(CN)(6)](4-) to the cobalt-ferrocyanide-impregnated fiber. The amount of [Fe(CN)(6)](4-) re-bound onto the fiber was found to decrease with increasing amount of Co-2[Fe(CN)(6)] initially impregnated. This suggests that the microparticles of cobalt ferrocyanide become entangled with the grafted polymer chains via multipoint electrostatic interactions.