Dimensionally stable, high surface area support for a possible direct methanol fuel cell application was fabricated from commercial diamond nanoparticles through electrophoretic deposition onto silicon wafer substrates, and their electrochemical characteristics were examined by employing inorganic redox probes such as [Fe (CN)6]3-/4- and [Ru (NH 3)6]3+/2+. As-received diamond nanoparticles were purified by refluxing in an aqueous nitric acid solution, and the product was characterized by using X-ray diffraction, X-ray photoelectron spectroscopy, prompt gamma-ray neutron activation analysis, Raman spectroscopy, electron energy loss spectroscopy, and transmission electron microscopy techniques. Electrophoretically deposited diamond nanoparticle layers of uniform thickness were obtained by controlling experimental parameters, such as applied voltage, deposition time, and the concentration of diamond nanoparticles in the suspension. Platinum nanoparticles were electrodeposited onto these diamond nanoparticle layers (Pt/DNP) by step and sweep potential method. Their structural and morphological characterizations were made by using scanning electron microscopy and energy-dispersive X-ray analysis. The electrochemical activity of Pt/DNP toward methanol oxidation was studied. The present study paves a way to fabricate ultrathin, uniform, high surface area, and dimensionally stable diamond electrodes in a controllable fashion. This type of deposited diamond nanoparticle layers may be considered as catalyst support material for fuel cell applications. © 2010 The Electrochemical Society.