An amperometric cell, using two comb-type electrodes, was examined for detection of gaseous hydrogen peroxide in air at room temperature. The planar-type sensor element was composed of the following cell: (cathode)Au/Nafion/Pt (anode). The cell current increased linearly with an increase in concentration of hydrogen peroxide at an applied voltage of 0.5 V (below the decomposition voltage of water). It was also found that the cell could respond sensitively with a fast response to gaseous hydrogen peroxide.