Composites of graphene decorated with silver nanoparticles were simply and efficiently synthesized using supercritical CO2. The nanoparticles were formed on graphene sheets through a simple hydrogen reduction of (1,5-Cyclooctadiene)(hexafluoroacetylacetonato) silver(I) precursor in supercritical CO2. The product was characterized by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, FTIR spectroscopy, X-ray diffraction, UV-visible spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Highly dispersed nanoparticles of varying size and shape were well adhered to graphene sheets. The composites showed high antibacterial activities against two Gram-negative bacteria Escherichia coli and Listonella anguillarum and two Gram-positive bacteria Bacillus cereus and Staphylococcus aureus. (c) 2012 Elsevier B.V. All rights reserved.