Ultrathin crystalline nanosheets give an extremely high surface area of a specific crystal facet with unique physical and chemical properties compared with normal three-dimensionally polyhedral nanocrystals (NCs). However, the ultrathin metal nanosheets tend to curl themselves or assemble with each other sheet by sheet, which may reduce the effective surface area and accordingly the catalytic activity to a great extent. Here we report a facile wet-chemical route that allows the fabrication of novel excavated rhombic dodecahedral (ERD) PtCu3 alloy NCs with ultrathin nanosheets of high-energy {110} facets. The surface area was measured to be 77 m(2) g(-1) by CO stripping, although the particle size is about 50 nm. Electrochemical characterizations showed that the ERD PtCu3 NCs exhibit excellent electrocatalytic performance and high antipoisoning activity in comparison with commercial Pt black and PtCu3 alloy NCs with {111} surfaces.