The main aim of the presented research was to obtain antibacterial fibers containing nanosilica with immobilized silver nanoparticles. The nanomodifier in an amount of 250 ppm, 500 ppm, 1,000 ppm, and 2,000 ppm were introduced into the cellulose fiber matrix during the cellulose dissolution process. In order to assess the influence of the nanomodifier's amount in the fiber on the antibacterial activity of modified fiber, a quantitative test of the antibacterial activity of the fibers was performed. The basic parameters of modified fibers, such as the mechanical and hygroscopic, were estimated. The size and shape of the nanomodifier in the selected fibers, as well as microanalysis of the polymer matrix, were examined. The investigations were conducted by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Energy Dispersive Spectrometry (EDS). The obtained results allowed the selection of optimal fibers with strong antibacterial properties that can be potentially used for personal protection or medical purposes.