Fabrication of high aspect ratio 3-nm Pt wires was achieved by reducing K2PtCl4 with dimethylamine borane in the presence of a tube-shaped tobacco mosaic virus. The presence of a nonionic detergent, Tween 20 in the reaction mixture prevents aggregation of the virus, and isolated Pt wires can be readily transferred onto silicon surfaces. Our results provide a new chemical approach to fabricate and locate 3-nm Pt wires on a substrate, which could not be achieved using conventional lithography.