Monodisperse single-crystalline sub-10 nm Pt-Pd nanotetrahedrons (NTs) and nanocubes (NCs) were synthesized with high shape selectivity via one-pot hydrothermal routes with small ions as efficient facet-selective agents. These alloy nanocrystals showed facet-dependent enhanced electrocatalytic activity and durability for methanol electrooxidations with commercial Pt/C catalyst as a reference. The (100)-facet-enclosed Pt-Pd NCs demonstrated a higher activity, whereas the (111)-facet-enclosed Pt-Pd NTs exhibited a better durability.