Functional polysiloxanes bearing both primary alcohols and quaternary ammonium salts (QAS) as lateral substituents were prepared. The synthesis involves a cohydrosilylation of allylic derivatives (N,N-dimethylallylamine and allyloxytrimethylsilane) with various poly(dimethylsiloxane-co-hydrogenomethylsiloxane)s. During the quaternization of the tertiary amino groups the alcohol functions are also deprotected. The hydroxyl groups allow the polysiloxane to be incorporated in polyurethane films whereas the QAS impart biocidal properties to the coating. In the case of a QAS bearing a hexadecyl substituent, a very high activity was found against Escherichia coli without any observable diffusion. The mode of action by contact between the solid polymer and the microorganisms was confirmed by the excellent durability of the biocidal power after 1 month of immersion in water.