Nowadays due to inefficiency of copper antibacterial activity, especially increasing resistance of bacteria towards copper, the use of copper particles in nano-scale is considered. According to the literature, limited studies have been performed on the applicability of these materials to control plant pathogenic bacteria. Aim of this study was to evaluate the antibacterial activity of copper nanoparticles (CuNPs) and copper-chitosan (Cu-Cs) nanocomposite on some important plant pathogenic bacteria. The nanoparticles were synthesized with sumac extract and their antibacterial activity in different concentrations was evaluated to determine their Minimum Inhibitory Concentration (MIC). The structure and physical properties of nanoparticles were characterized by Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), and UV-Visible spectroscopy. Results showed that the CuNPs and nanocomposite had quasi-spherical shape in a uniform distribution with the average size of 100 and 20nm respectively. Green biosynthesized CuNPs showed minimum inhibitory concentration against Xanthomonas perforans, Clavibacter michiganensis subsp. michiganensis, Erwinia amylovora and Pseudomonas syringae pv. syringae at concentrations 0.5 ppm, 0.5ppm, 1ppm and 1.5ppm respectively. Also, Cu-Cs nanocomposite had an effective antibacterial activity at higher concentrations than copper nanoparticles. The lowest inhibitory concentration of nanocomposite was for X. perforans in combination of 1ppm CuNP and 3.93ppm Chitosan. However, chitosan did not increase the antibacterial activity of copper nanoparticles and no synergistic effect was observed for this compound.