A planar-structure methanol sensor capable of detecting methanol concentration of 0-2 M was demonstrated. A proton-conducting polymer, recast Nafion 117 perfluorosulfonic acid membrane, was employed as the electrolyte in this work. Thick film technology by screen-printing defined gold layers on an alumina substrate was used for the working and the counter electrodes. A silver/silver chloride electrode was used as the reference electrode. There were inlet holes in the working electrode allowing methanol aqueous solution to move easily through the porous membrane and diffuse onto the electrode surface, where the methanol was decomposed, yielding an oxidation current. Electrochemical impedance spectroscopy and cyclic voltammetry (CV) were used to define the electrochemical characteristics of the sensor. The CV results revealed that the oxidation current had two peaks, illustrating, respectively, the hydrogen desorption at similar to 0.22 V-SHE and the methanol oxidation at similar to 1.0 V-SHE (where SHE denotes standard hydrogen electrode). The current output of hydrogen desorption appeared to be reversely proportional to the methanol concentration in 0-2 M. (c) 2006 The Electrochemical Society.