Enhanced photocatalytic disinfection of Escherichia coli (E. coli) bacteria under visible light illumination was achieved by a silver-modified nitrogen-doped titanium oxide (TiON/Ag2O) nanoparticle photocatalyst synthesized by a sol-gel process. In this photocatalytic material system, silver additives are beneficial to achieve better crystallization, larger surface area, higher pore volume, and enhanced visible light absorbance. The enhanced photocatalytic disinfection of E. coli by TiON/Ag2O was proven to be mostly attributed to the photocatalytic response of the TiON matrix and the subsequent coupling between TiON matrix and Ag2O nanoparticles, not the silver addition itself. The optimized silver modification concentration is determined at an Ag:Ti molar ratio of 1:50.