A novel brush-type microbial-cell-adsorbing material was prepared by radiation-induced graft polymerization. A vinyl monomer containing an epoxy group, glycidyl methacrylate (GMA), was first grafted onto a polyethylene-based fiber before the introduction of a tertiary amino group, i.e., diethylamine (DEA). The grafted-type DEA fibers prepared were then tested for their microbial-cell-adsorbing activity by contacting the fibers with a Staphylococcus aureus suspension. The DEA fibers showed adsorption ability of S. aureus, and the adsorption rate increased with increasing density of the DEA group. On the other hand, DEA was also introduced onto crosslinked-type GMA beads and its adsorption rate of S. aureus cells was compared with that of the grafted-type DEA fibers. The grafted-type DEA fibers exhibited an adsorption rate constant 1000-fold greater than that of the cross-linked-type DEA beads. Observation by scanning electron microscopy showed that the shape of S. aureus cells adsorbed on the grafted-type DEA fibers was intact whereas the shape of those adsorbed on the cross-linked-type DEA beads was difficult to identify.