Structural changes at various Pt single crystal surfaces of higher Miller index before and after many potential cycles were examined with in situ STM and cyclic voltammetry in acidic and alkaline solutions. STM images at Pt(111), Pt(100) and Pt(210) after 100 potential cycles in 0.05 M H2SO4 solution were observed. Many islands of platinum atoms on the terraces of Pt(111) and Pt(100) were found after the potential cycles, but not on Pt(210). The Pt(210) surface is changed with more difficulty with potential cycling than the Pt(111) and Pt(100) surfaces. Voltammograms for surfaces of higher Miller index after 500 potential cycles were examined. The sharp peaks of the hydrogen desorption wave become wider after the potential cycles. After the potential cycles, the shape of the voltammograms at Pt(111) and Pt(110) groups change into that at Pt(320) or Pt(530). The shapes of the voltammograms at Pt(100) groups change into that at Pt(310) after the potential cycles.