The selective growth of Au nanoparticles on (111) facets of truncated octahedral and cuboctahedral Cu2O crystals has been achieved by exploiting the differences in the standard potential between AuCl4-/Au and Cu2+/Cu2O pairs and in surface energies between (111) and (100) planes. The density and size of Au nanoparticles can be controlled by tuning the concentration of the gold precursor. Truncated octahedral Cu2O-Au nanocomposites have a 10 times higher electrochemically catalytic activity toward H2O2 reduction than do pure Cu2O crystals. The enhanced catalysis may be derived from the polarization of Au NPs at the interface, which makes Cu2O more active for H2O2 reduction.