Plant diseases pose a major threat to global food security and environmental sustainability. As climate change worsens, the risks of disease outbreaks and the emergence of new strains of plant pathogens increase. Bacteria are among the most important plant pathogens and have a significant economic impact. Traditional bactericides, such as antibiotics and copper compounds, can cause environmental and health damage and contribute to the emergence of bactericide-resistant bacterial pathogens. Hence, the importance of metal nanoparticles as a promising tool to combat bacterial pathogens, especially bactericide-resistant strains. Metallic nanoparticles exhibit new or improved physical and chemical properties that increase their effectiveness against target organisms and reduce toxicity to non-target organisms. Several nanoparticles (NPs), most notably silver, copper, copper oxide, and zinc oxide NPs, exhibit antibacterial activity against important bacterial plant pathogens. Experiments have shown that nanobactericides can be applied in many agricultural systems and with different application methods to combat bacterial diseases of plants. Given the growing need to use metallic NPs to combat plant diseases, it is important to consider their effects on plants. Despite the evident benefits of using nanomaterials on plants, high doses may cause phytotoxicity. This chapter focuses on the most important metal-based nanomaterials (mNMs) used in combating bacterial plant diseases, their applications, and morpho-physiological responses to plants.