Size-controlled gold nanocrystals were conveniently synthesized through direct electroreduction of bulk AuCl(4)(-) ions in the presence of poly(N-vinylpyrrolidone) (PVP). PVP greatly enhanced the gold particle formation process and also significantly retarded the gold electrodeposition process, allowing the electrochemical synthesis of gold nanocrystals to be carried out in the form of simple electroreduction. This novel electrochemical method may be extended to synthesis of other noble metal nanoparticles with controllable size on a large scale. The PVPK90-protected gold nanocrystals spontaneously self-assembled into nearly ordered 2D close-packed arrays and interesting 1D nanostructures. The aggregation of unstable PVPK17-protected gold nanocrystals resulted in the formation of ultrathin single-crystalline films. PVP plays multifunctional roles in controlling the size and shape of gold nanocrystals and in inducing individual gold nanocrystals to construct 1D nanostructures. The nanoparticle self-assembling technique based on PVP offers a simple, but effective, path to organize individual gold nanoparticles into various 1D and 2D nanostructured materials.