Biocidal poly(oxyethylene)s with N-halamine side groups were prepared using polymer analogous reactions of poly[oxy(chloromethyl)ethylene] with 5,5-dimethylhydantoin followed by chlorination. The biocidal poly(oxyethylene) films effectively inactivated the gram-negative bacteria Escherichia coli and maintained their biocidal property after long-term (3-month) storage. Since biocidal poly(oxyethylene) films have antibacterial efficacy and stability on hard surfaces, they could be useful in a variety of household and medical antibacterial applications.