A simple method was developed to load a large amount of silver nanoparticles into bacterial cellulose (BC) produced by Gluconacetobacter xylinus in a controlled manner. Due to the high electron-rich oxygen density in the BC macromolecules and the large surface area of the BC nanoporous structure as an effective nanoreactor, the in situ direct metallization technique was successfully used to synthesize Ag nanoparticles with an average diameter of 30 nm and a loading content of at least 5 wt. (%), approximately. This novel procedure provides an easy and economical way to manufacture Ag nanoparticles supported on a porous membrane for various biomedical applications. These composite fibers showed nearly 100% antibacterial activity (elimination of microorganisms) against Escherichia coli because of the presence of the silver nanoparticles.