Two types of homopolymers {poly[tributyl(4-vinylbenzyl)phosphonium chloride] and poly [ tributyl (4-vinylbenzyl) ammonium chloride]} and copolymers, in which the compositional ratio of the phosphonium monomer to the ammonium monomer was altered. were prepared. The antibacterial activities of both the mixtures of the homopolymers in which the mixing ratio was altered and the copolymers containing positively charged phosphorus and nitrogen atoms in a single polymer chain were explored by the viable cell counting method in sterile distilled water. In the mixed system, a significant finding was the presence of an optimal mixing ratio for the antibacterial activity. The mixtures of polymeric phosphonium salt and polymeric ammonium salt clearly showed the synergistic effect on the antibacterial activity. On the other hand, the antibacterial activity of the copolymers with different cationic parts increased monotonously with increasing the phosphonium monomer units in the polymers, namely, the incorporation of two types of active moieties into a single molecule seems to be unfavorable for synergism on the antibacterial activity.