Monodisperse 8 nm Pt nanocubes are synthesized by reducing Pt(acac)(2) in the presence of oleic acid, oleylamine, and a trace amount of Fe(CO)(5). Self-assembly of these nanocubes results in a (100) textured array. The nanocubes show an enhanced catalysis toward oxygen reduction, and their specific activity is over twice as high as that from the commercial Pt nanoparticles.