Structural effects on the hydrogen oxidation reactions (HOR) and the hydrogen evolution reactions (HER) have been studied on (n-1)(1 1 1)-(1 1 0), n(1 0 0)-(1 1 1), n(1 0 0)-(1 1 0) and n(1 1 1)-(1 0 0) series of Pt using rotating disk electrode (RDE) in 0.1 M HClO(4) saturated with H(2). The value of the exchange current density J(0) increases linearly with the increase of the step atom density d(S) from n = infinity to n = 9, where n denotes the number of terrace atomic rows, on (n-1)(1 1 1)-(1 1 0), n(1 0 0)-(1 1 1), and n(1 0 0)-(1 1 0) series. This indicates that the activity for the HOR/HER of the step is higher than that of the terrace. The values of j(0) of (n-1)(1 1 1)-(1 1 0), n(1 0 0)-(1 1 1) and n(1 0 0)-(1 1 0) series become constant on the surfaces with n <= 9, whereas those of n(1 1 1)-(1 0 0) series increase with the increase of d(S). The activity for the HOR/HER per step atom increases in the sequence: n(1 1 1)-(1 0 0) < n(1 0 0)-(1 1 1) < n(1 0 0)-(1 1 0) < (n-1)(1 1 1)-(1 1 0). This result supports that the most active site for the HOR/HER is the linear (1 1 0) step. Decrease of the NOR current is found around 0.2 V(RHE) on the surfaces with (1 0 0) terrace, whereas the surfaces with (1 1 1) terrace give no decrease of the HOR current. (C) 2011 Elsevier B.V. All rights reserved.