Oxygen reduction reaction (ORR) activities of Pt/Au(111) and Pt/Au(100) bimetallic surfaces prepared using molecular beam epitaxy were evaluated in this study. Surface structures of the bimetallic surfaces were verified using a scanning tunneling microscope under ultra-high vacuum conditions. The deposition of a 0.3-nm-thick Pt on a clean Au(111) at 300 K (300K-Pt0.3nm/ Au(111)) generated a corrugated Pt(111) epitaxial layer on which monoatomic-height Pt islands are present. The ORR activity estimated from the kinetically controlled current density at 0.9 V vs. RHE was ca. two times greater than that of the clean Pt(111). In contrast, the 473K-Pt 0.3nm/Au(111) as well as 300K-Pt0.3nm/Au(100) exhibited small hydrogen-related charges, thereby were less ORR active than the corresponding clean Pt substrate surfaces. These results suggest that atomic arrangements of surface Pt atoms, particularly the morphologies of the most dense plane of Pt(111), correlate with the enhancement in the ORR activity of Pt-u bimetallic nanoparticles.