Abstract: Copper nanoparticles encapsulated by carbon (Cu-NPs@C) were synthesized by a two-step method by mixing cupric chloride and glucose in a solution, followed by carbonization. The microstructures and antibacterial activities of the Cu-NPs@C samples were characterized by TEM, XRD, XPS, nitrogen adsorption and antibacterial activity tests. Results indicated that the as-synthesized Cu-NPs had a FCC crystal structure and a spherical morphology of diameter 4-46 nm and were well dispersed in the porous graphitic carbon layers. When the mass ratio of cupric chloride to glucose was less than 1:5, the Cu-NPs@C were of pure metallic copper without any oxides, and were stable against ambient air oxidation. The Cu-NPs@C synthesized with a mass ratio of cupric chloride to glucose of 1:5 had a specific surface area of 418 m²/g, which showed much higher antibacterial activities against three different common bacteria (Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa) than pure nano-copper powder. It was believed that the carbon layers are responsible for capturing the bacteria while the copper ions released from the copper nanoparticles kill them. The outer carbon layers effectively protected the metallic copper inside from oxidation. These findings indicate that Cu-NPs@C can be used as a stable antibacterial agent in biomedical applications.