Metal nanostructured materials have been the focus of much scientific research for decades because of their unusual optical, electronic, magnetic, catalytic, and other properties that are distinctly different from their bulk counterparts, and therefore, considerable attention from both fundamental and applied research has been paid to the synthesis and characterization of these materials. Particular interest has been focused on the noble metal nanoparticles because of their unique optical and electrical properties and interesting applications of the nanoparticles in many fields such as catalysis, optics, sensors, and surface enhanced Raman spectroscopy. Controlling the nanoparticle shape is technologically important, since the optical, electronic, magnetic, and catalytic properties of nanomaterials depend critically not only on particle size but also on particle shape. Several methods have been developed for preparing nanoparticles in a variety of shapes, including rods, prisms, wires, and disks. Recently, two-dimensional gold nanoplates have attracted increasing attention because of their potential applications in the areas of electrochemistry and producing new nanodevices. The preparation of nanoplates with controlled size and thickness has been continuously reported by using various synthesis methods. For instance, Lee et al. and Chen et al. prepared gold sheets of about 10 μm by thermal reduction of HAuCl4 in the bulk phase of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer. Dong et al. and Sastry et al. prepared gold nanoplates of about 1 μm by aspartate or ortho-phenylenediamine reduction of HAuCl4 and by biological method, respectively. In this work, we present a study of the photosynthesis of gold nanoplates at the water/oil interface without any additional templates, surfactants, and reducing agents. We found that hexagonal and truncated triangular crystalline gold nanoplates can be easily formed by irradiating biphasic mixture consists of diethyl ether and aqueous gold salt solution with a conventional fluorescent light. The physicochemical characteristics of the prepared nanoparticles were examined by various analytical tools such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS).