The structural effect on the rate of CO2 reduction was studied with voltammograms on Pt(S)-[n(111)x(100)] and Pt(S)-[n(100)x(111)] electrodes in 0.1 M HClO4. The surfaces with higher step density gave higher rates of CO2 reduction, as is the case of Pt(S)-[n(111)x(111)] reported previously. The electrodes with (111) step show higher activity for CO2 reduction than those with (100) step. Pt(S)-[n(111)x(100)] and Pt(S)[n(100)x(111)] give minimum rates at 0.25 V. This potential dependence differs remarkably from that on Pt(S)-[n(111) x(111)] on which the rates have maxima at 0.20 V. The following order of the activity for CO2 reduction was obtained : Pt(S)-[n(111)x(100)] < Pt(S)-[n(100)x(111)] < Pt(S)-[n(111)x(111)]. Pt(110) gave the highest rate of CO2 reduction of all the examined surfaces. The atomic arrangement that enhances the activity for CO2 reduction is discussed.