The oxygen reduction reaction (ORR) have been studied on n(1 1 1)-(1 0 0) series of Pd using hanging meniscus rotating disk electrode (HMRDE) in 0.1 m HClO(4) saturated with O(2). Activity for the ORR, which is estimated by the reduction current density at 0.90 V (RHE) j(ORR,0.90V). is enhanced linearly with the increase of the terrace atom density d(T), showing that (1 1 1) terrace is the active site for the ORR on n(1 1 1)-(1 0 0) series of Pd. Coverage of the oxide film theta(OX) of Pd increases with the increase of d(T) at 0.90 V (RHE). The correlation of the ORR activity and theta(OX) contradicts to that on Pt electrodes on which the ORR is deactivated with the increase of theta(OX) The oxide film is not relevant to the ORR on n(1 1 1)-(1 0 0) series of Pd at 0.90 V (RHE). (C) 2011 Elsevier B.V. All rights reserved.