Phosphonium salts with different alkyl chains as substituents were incorporated covalently on the surfaces of cellulose filters with silane coupling agents containing phosphonium ions, and their surface antibacterial activities against Staphylococcus aureus and Escherichia coli were explored by the viable cell-counting method in sterile distilled water. The filters incorporating phosphonium biocides showed higher antibacterial activity, and its activity strongly depended on the structure of substitutuents. The surface-treated filters may be used to sterilize air and water, including microorganisms.