Commercial ultrafiltration membranes were modified using different polymeric nanofibers in order to gain additional water treatment functionality. Membrane surfaces were given biocidal properties by adding electrospun nanofiber structures containing various forms of silver. Changes in viscosity and homogeneity of the electrospinning solution caused by the additives limited the amount of silver that could be added; hence, electrospinning conditions were optimized to maximize silver particle content. Best results were obtained using highly soluble silver nitrate and silver benzoate as silver nanoparticle precursors. The biocidal properties of the modified membranes were confirmed through cultivation techniques and respirometry, with the results indicating that ultrafiltration membranes modification using silver-treated nanofibers is a promising technique.