A simple and facile synthesis of gold nanowire networks and sol particles at room temperature is presented using L-tyrosine (Tyr) as both the reducing and capping agent. The synthesis conditions with varying the gold precursor concentration ([HAuCl4], 0.1-2.5 mM) and concentration ratio of tyrosine to gold precursor R ([Tyr]/[HAuCl4], 0.05-10) were identified for the preparation of network-like nanowires and sol nanoparticles. Gold sol particles with sizes between 10 and 18 nm were mostly obtained at R > or = 0.2. Network-like gold nanowires with average diameters as thin as 8 nm can be reproducibly synthesized at R < or = 0.1. The experimental data revealed that the phenolic and carboxyl group of Tyr were oxidized to form quinone and alcohol, respectively. The growth process was examined to elucidate the influence of the synthesis conditions on different morphologies, showing marked difference in isotropic and anisotropic growth of gold nanostructures at different synthesis conditions. The study showed that tyrosine possesses excellent reducing capability with short nucleation period and long growth period as compared with other amino acids.