We report direct synthesis of Ag/PVP nanocomposites using PVP (polyvinylpyrrolidone) as a reducing agent. Ag/PVP nanocomposites were synthesized after mixing PVP with acetone and a small amount of aqueous silver nitrate (AgNO(3)) under magnetic stirring. The Ag/PVP colloids were then dissolved in water (sample 1) and in ethylene glycol (sample 2) and stirred for 10 days. UV/vis spectra show surface plasmon band in the visible region, centered at wavelengths between 435 and 445 nm, a clear consequence of the nano size of dilute Ag particles. TEM results showed that the Ag/PVP nanocomposites have particle sizes ranging from 1 to 6 nm and 1 to 12 nm for colloids in water and ethylene glycol respectively. Antibacterial activity of these silver nanocomposites as a function of particles concentration against gram-negative bacterium Escherichia coli (E. coli) was carried out in solid growth media. Both the nanocomposites showed good antibacterial activity and caused a growth delay of E. coli with zone of inhibition similar to 16 mm. There was very little difference between antibacterial activities of two types of silver nanocomposites, though sample 1 with smaller size showed a slightly better antibacterial action. (C) 2010 Elsevier B. V. All rights reserved.