An environmentally friendly method using a cell-free extract (CFE) of Rhodopseudomonas capsulata is proposed to synthesize gold nanowires with a network structure. This procedure offers control over the shapes of gold nanoparticles with the change of HAuCl4 concentration. The CFE solutions were added with different concentrations of HAuCl4, resulting in the bioreduction of gold ions and biosynthesis of morphologies of gold nanostructures. It is probable that proteins acted as the major biomolecules involved in the bioreduction and synthesis of gold nanoparticles. At a lower concentration of gold ions, exclusively spherical gold nanoparticles with sizes ranging from 10 to 20 nm were produced, whereas gold nanowires with a network structure formed at the higher concentration of gold ions in the aqueous solution. This method is expected to be applicable to the synthesis of other metallic nanowires such as silver and platinum, and even other anisotropic metal nanostructures are expected using the biosynthetic methods.