A complex of Ag/AgCl nanoparticles was synthesized on the basis of the extracellular polysaccharide of Azotobacter chroococcum XU1 and 10 mM AgNO3 solution. The complex was characterized by UV spectroscopy, X-ray diffraction, and scanning electron microscopy. Colloidal solutions of the complex had absorption peaks at 260 and 420 nm, indicating the formation Ag/AgCl nanoparticles. The size of the nanoparticles varied from 6 to 50 nm. The nanobiocomposite consisting of the exopolysaccharide matrix and Ag/AgCl nanoparticles exhibited a fungicidal effect against such plant pathogens as Fusarium oxysporum f. sp. vasinfectum and Verticillium dahliae.