Silver nanoparticles were prepared from a polyacrylonitrile (PAN) /N,N-dimethylformamide solution of silver nitrate (0.05-0.5 wt %) with light treatment (xenon arc) to reduce Ag(+) ions into Ag(0). The formation of silver nanoparticles in the PAN solution and the effect of treatment time on the numbers of silver nanoparticles, their average diameter and size distribution were investigated by UV-visible spectroscopy. In addition, the average size of silver nanoparticles and their shapes in colloidal solution were determined by transmission electron microscopy images and found to be on the order of 1.0 nm. The resulting solution was electrospun into PAN nanofibers. An increase in the salt concentration led to decreases in the nanofiber diameter and bead numbers (determined by scanning electron microscopy images) and an increase in the crystallinity (confirmed by X-ray diffraction patterns). A continuous rate of silver release from the nanofiber web was monitored by the atomic absorption technique. These nanofibers showed strong antibacterial activity against Pseudomonas aeruginosa. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1021-1029, 2010