A novel antibacterial agent (CF-BTx-nAg) of nanometer silver (nAg) was synthesized by using bayberry tannin (BT) grafted collagen fiber (CF) as supporting. Bayberry tannin (BT), a typical natural polyphenol, was grafted onto the CF surface to improve the loading capacity and to control the size as well as the dispersion of Ag nanoparticles. The main physical and chemical properties of this antibacterial agent were characterized by means of Scanning Electron Microscopy (SEM), Fourier Transform-Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS) and X-ray Diffraction (XRD). It was found that this antibacterial agent is in highly ordered fibrous state. The average diameter of Ag nanoparticles is 3.25 nm and the nanoparticles are homogeneously dispersed. Antibacterial experiments demonstrated that CF-BTx-nAg exhibited high antibacterial activity. When cell suspensions of Escherichia coil solutions with concentration of ~105 cfu/mL was cultivated with CF-BT0.2-nAg at 310 K under shaking (150 r/min, conc. of Ag = 8 μg/mL), the number of living cells went down to zero within 4 h, while it was 8 h and 12 h for that of CF-BT0.05-nAg and CF-BT1.0-nAg, respectively. The minimal inhibitory concentration (MIC) of CF-BT0.2-nAg against E. coli was 4 μg Ag/mL. In addition, CF-BT0.2-nAg can be re-applicated effectively at least five times. These facts suggested that CF-BT-nAg could be used as a new and effective antibacterial agent.