In this study, we investigated the antimicrobial activity of silver nanoparticles (Ag-NPs) and platinum nanoparticles (Pt-NPs) aqueous solution, which were prepared using different stabilizer, such as sodium dodecylsulfate (SDS) and poly-(N-vinyl-2-pyrrolidone) (PVP), for Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) by measuring the minimum inhibitory concentration (MIC). Antimicrobial effect of Ag-NPs for S. aureus and E coli was investigated using cup diffusion method. The growth of Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria were inhibited by Ag-NPs. The MIC of Ag-NPs for S. aureus and E. coli were 5 and 10 ppm, respectively. But the Au-NPs stabilized with SDS did not show antimicrobial activity. Also, the Pt-NPs stabilized with PVP (or SDS) did not show antimicrobial activity for the test organisms. (C) 2005 Elsevier Ltd. All rights reserved.